UKSEF Reporting Software for UK-Listed Companies
UKSEF is the UK Single Electronic Format, the UK’s variant of the European Single Electronic Format (ESEF), maintained by the Financial Reporting Council (FRC) and designed for companies listed on UK regulated markets.
The UKSEF taxonomy is an expansion of the ESEF taxonomy which is accepted by the Financial Conduct Authority (FCA), incorporating UK-specific tags (UKSEF elements) required by Companies House.
UK-listed companies can file UKSEF to meet the requirements of both the FCA (the UK’s Financial Conduct Authority) and Companies House, with the FCA overseeing the electronic reporting process. Companies that file in UKSEF can apply the UK-specific tagging, which covers areas such as Companies House registration information, the Strategic Report, the Directors’ report, the Auditor’s report, the Streamlined Energy and Carbon Reporting disclosures and parent company financial statements. Filers can submit the same report to both the FCA and Companies House.
What Is UKSEF?
UKSEF was introduced by the Financial Reporting Council in 2021 as the UK’s variant of the European Single Electronic Format (ESEF), designed to meet specific regulatory requirements for financial reporting in the UK. The country’s withdrawal from the EU led to the development of UKSEF, which builds upon the original ESEF requirements to address UK-specific regulatory needs. It uses the same iXBRL tagging model as ESEF, built on the same underlying IFRS taxonomy, with added tags stemming from the FRC’s own suite of taxonomies.
Compliance falls under the FCA’s DTR 4.1 rules and applies to financial years starting on or after 1 January 2021.
Who Is Required to Comply with UKSEF?
The FCA requires issuers with transferable securities admitted to trading on a UK-regulated market to file annual reports in digital format, in line with specific reporting requirements for companies listed on UK regulated markets. In practice, this means companies on the Main Market of the London Stock Exchange.
AIM-listed companies and those on unregulated markets are out of scope. UK-incorporated and overseas issuers with primary listings in the UK are both included.
In-scope issuers can file in either UKSEF or ESEF. UKSEF is the broader option and its adoption is currently on an upward trajectory. It’s preferred by those wanting one filing to cover both their FCA and Companies House obligations.
UKSEF and the FCA’s National Storage Mechanism (NSM)
The NSM is the FCA’s official register for regulated information. UKSEF regulatory filings are submitted through the FCA’s Electronic Submission System and published on the NSM for public access, ensuring that all submissions meet the required technical standards for electronic reporting.
The NSM validates each filing against technical and business rules on submission. Errors prevent acceptance, while warnings flag potential issues for the filer to review.
UKSEF vs ESEF – What’s the Difference?
Both UKSEF and ESEF are based on a standardised classification system, which promotes uniformity and comparability in reporting. This ensures compliance with ESEF requirements and international financial reporting standards, making it easier to review, detect mistakes, and prevent fraud. Both formats produce XHTML annual reports with iXBRL tags on the consolidated financial statements, both build on the IFRS taxonomy, and the FCA accepts both at the NSM. The UKSEF vs ESEF question is about what UKSEF adds on top.
UKSEF covers additional areas such as Companies House registration information, the Strategic Report, the Directors’ report, the Auditor’s report, the Streamlined Energy and Carbon Reporting disclosures and parent company financial statements. UKSEF satisfies the Companies House validations that are needed for the document to be accepted at its digital gateway.
Both formats require the use of inline XBRL (iXBRL) for tagging financial information, but UKSEF includes additional UK-specific tags to comply with Companies House requirements. Both taxonomies support the new IFRS 18 standard and other recent changes to IFRSs.
What Does UKSEF Compliance Require?
A compliant UKSEF filing ensures statutory reporting obligations are met through a streamlined UKSEF reporting process, which covers the XHTML report format, UKSEF iXBRL tagging on the financial statements, any UK-specific disclosures, and submission to the FCA and Companies House. This process ensures that annual financial reports are machine readable, supporting regulatory compliance and efficient data processing. UKSEF, like ESEF, requires companies to prepare their annual financial reports using inline XBRL (iXBRL) for consolidated reporting and XHTML for solo reporting, enhancing data accessibility and compliance checks. UKSEF reporting software handles the conversion, tagging, and validation in a single workflow.
XHTML Format for Your Annual Financial Report
While annual reports were traditionally produced in PDF format, which limited data analysis and regulatory compliance due to its lack of machine readability, UKSEF now requires the annual report to be filed as an XHTML document. This ensures that financial data is both human-readable and machine-readable for compliance. Companies can keep the visual design of their annual report intact while embedding the iXBRL data underneath.
iXBRL Tagging for Consolidated IFRS Financial Statements
The consolidated income statement, balance sheet, cash flow, and statement of changes in equity get line-by-line tagging from the UKSEF taxonomy, which involves converting financial statements into iXBRL format. iXBRL conversion is a key step in preparing compliant filings, ensuring that financial data is machine-readable and meets regulatory requirements. Notes to the financial statements are tagged in blocks of related disclosure.
SECR Disclosures (UK Specific)
Streamlined Energy and Carbon Reporting (SECR) requires UK quoted companies and large unquoted companies to disclose energy use, greenhouse gas emissions, and at least one intensity ratio in their annual report. These SECR disclosures contribute to sustainability data and support corporate sustainability objectives, aligning with the evolving regulatory landscape shaped by initiatives such as the Corporate Sustainability Reporting Directive (CSRD). Tagging these disclosures is voluntary. UKSEF enables the tagging of these disclosures directly, while ESEF does not provide the relevant tags in its taxonomy.
Filing with Both the FCA and Companies House
Public companies must ensure their annual financial statements meet the requirements for regulatory filings with both the FCA and Companies House. UKSEF can be filed with both UK regulators. The taxonomy includes the registered number and period end date Companies House requires alongside the FCA’s filing requirements at the NSM, which means one report can serve both filings.
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Seahorse – CoreFiling’s UKSEF Reporting Software
Seahorse is our UKSEF reporting software for LSE-listed companies, delivered as SaaS for in-house teams and tagging service partners. Trusted by accounting firms for its reliability, Seahorse helps reduce risk in the reporting process by ensuring compliance with regulatory requirements. It converts source documents, supports AI-assisted tag selection from the UKSEF taxonomy, and validates against the rules the FRC publishes and the FCA enforces at the NSM. High-quality UKSEF tools like Seahorse also provide capabilities for switching between the UKSEF and EU-based ESEF taxonomies.
Convert Your Annual Report to UKSEF iXBRL
You upload the annual report in Word, Excel, PDF, or InDesign and Seahorse converts it to XHTML immediately. This conversion process is similar to the one now required for company tax returns, which must be submitted in iXBRL format instead of PDF to comply with HMRC regulations. The visual layout is preserved through the conversion, so the filed document keeps the design of the source.
AI-Assisted iXBRL Tag Selection by the UKSEF Taxonomy
For each line of the financial statements, Seahorse suggests UKSEF tags based on hundreds of prior filings. When company specific information is not covered by standard tags, extension elements are used to ensure all disclosures are properly tagged. Each suggestion comes with a confidence score and can be accepted, refined, or rejected.
Block Tagging for Notes to Financial Statements
Notes to the financial statements are tagged in blocks of related disclosure rather than line by line. Seahorse supports both block tagging and nested block tagging, which applies where one tagged section sits inside another.
Built-in Validation Against FRC Filing Rules
Filings are validated against the FRC’s UKSEF rules and the FCA’s technical guidelines as the document is built, with built-in validation checks ensuring compliance with the Conformance Suite—a draft and standardised framework created by the FCA and FRC for UKSEF reporting. Errors and warnings surface in the interface so they can be resolved before submission to the NSM.
Roll-Over Tagging – Carry Forward Prior Year Decisions
After the first filing, prior-year tagging decisions can be rolled forward into the current report. Most line items keep the same tags from one year to the next, which removes the bulk of the manual work in subsequent cycles.
Multi-Target Document Support – File to FCA and Companies House in One Report
The same UKSEF filing produced in Seahorse can be submitted to both the FCA’s NSM and Companies House. The taxonomy includes the identifiers Companies House requires, and the output is packaged correctly for each destination.
Supported Input Formats
Seahorse takes annual reports in the source formats most companies already use, so the upstream production process doesn’t need to change to fit the software.
PDF, Word, Excel and InDesign – All Supported
Annual reports built in PDF, Word, Excel, or InDesign all upload directly to Seahorse and convert to XHTML on the way in. Whether the report is produced by an in-house finance team or an external design agency, the source file goes straight to the software.
UKSEF Tagging Services – Our UK Partner Network
The CoreFiling partner network in the UK is made up of accountancy-trained tagging specialists who work with Seahorse on behalf of filers. The model suits companies that don’t have iXBRL experience in-house, or whose finance teams are stretched at year-end.
Find a Certified UKSEF Tagging Service Provider in the UK
UK partners deliver Seahorse-based tagging services for both UKSEF and ESEF filings. Companies hand over the source document in Word, Excel, PDF, or InDesign and receive a fully tagged, FCA-ready filing back, with judgement decisions documented for review.
Many partners also support a phased transition to in-house tagging in later years. The first year’s tagging work rolls forward into Seahorse for the company to take over directly.
Why CoreFiling for UKSEF Reporting?
CoreFiling co-invented iXBRL with HMRC, contributes to UKSEF taxonomy development at the FRC, and supplies validation technology that UK regulators use to process incoming filings. The company has been working in iXBRL and structured reporting for more than two decades.
Invented iXBRL with HMRC:
iXBRL was co-developed by CoreFiling and HMRC in the late 2000s and adopted in 2010 for UK Corporation Tax filings. The format is now used in mandates around the world, including ESEF and UKSEF in Europe and SEC filings in the US.
Build UKSEF into your own product:
For software vendors that want to build UKSEF capability into their own products, CoreFiling provides API access to the True North platform. The integration model lets disclosure management tools, ERP systems, and reporting platforms call Seahorse-grade tagging and validation directly.
The same engine Companies House use:
The True North validation engine inside Seahorse is the same software Companies House use to process incoming UK corporate filings. Validation results in Seahorse match what regulators see when the filing is submitted.
A hand in shaping the UKSEF taxonomy:
CoreFiling contributes directly to UKSEF taxonomy development at the FRC. Seahorse tracks taxonomy changes quickly because the same team that helps draft them also maintains the software.
In XBRL since 1997:
CoreFiling has been working on XBRL and iXBRL for more than 25 years. The company’s technology has processed over £2 trillion in UK taxes, three million corporate filings, and five million XBRL documents to date.
Certified for security and compliance:
Seahorse holds XBRL International’s Report Creation Software certification, the formal mark of compliance with the technical standard. CoreFiling holds ISO 27001 certification for information security, which matters when filings include unpublished financial data.
UKSEF Reporting Software FAQs
We’ve taken some time to answer some common questions about our XBRL and iXBRL services.
What Is UKSEF Reporting Software?
UKSEF reporting software converts an annual financial report from formats like Word, Excel, PDF, or InDesign into the XHTML and iXBRL output the FCA accepts at its National Storage Mechanism. It applies the UKSEF taxonomy tags to the consolidated financial statements and validates the result against FRC filing rules.
Is UKSEF Mandatory for LSE-Listed Companies?
UKSEF is one of two compliant filing formats for LSE-listed companies, alongside ESEF. The FCA requires Main Market issuers to file in one of the two formats, and many UK filers prefer UKSEF because it adds tags for SECR and Companies House submissions.
Can I Use Either ESEF or UKSEF to File with the FCA?
The FCA accepts annual financial reports in either UKSEF or ESEF. Both formats go through the same Electronic Submission System into the NSM, and the choice usually comes down to whether you need to tag UK-specific disclosures or file a single document at Companies House.
What Is the UKSEF Taxonomy and How Does It Differ from ESEF?
The UKSEF taxonomy is the FRC-maintained dictionary of tags used in UKSEF filings. It includes everything in the ESEF taxonomy plus additional taxonomy sections drawn from the FRC taxonomies that cover Companies House requirements, such as the company’s registered number, the period end date, and sections that cover the Strategic report, the Directors’ report, the Audit report and parent company financial statements as well as the SECR regulation.
What Are SECR Tagging Requirements Under UKSEF?
Companies in scope of SECR must disclose energy use, greenhouse gas emissions, and at least one intensity ratio inside their annual report. Under UKSEF, those disclosures can be tagged in the same way as the financial statements, so the carbon and energy data becomes machine-readable alongside the financial figures. Tagging these disclosures is voluntary at this stage.
How Does Seahorse Validate Against UKSEF Conformance Rules?
Seahorse validates each filing against the FRC’s UKSEF filing manual and the FCA’s technical guidelines at the NSM. The same True North validation engine runs inside Companies House for UK corporate filings, so the results Seahorse shows match what regulators see when the document is submitted.
Can I File the Same Report to Both the FCA and Companies House?
The same UKSEF filing can be submitted to both the FCA’s NSM and Companies House. UKSEF includes tags for the company’s registered number and period end date that Companies House requires at its digital gateway, so the same document serves both regulators without re-tagging or repackaging.
Ready to File Your UKSEF Report?
LSE-listed companies need UKSEF reporting software that handles UK-specific tagging, files to both UK regulators, and validates against the rules the FRC publishes. Seahorse does this work in a single platform, with a UK partner network for filers who want to outsource.
With Seahorse, you can:
Tag the disclosures ESEF can't reach:
The Strategic report, the Directors’ report, Auditor’s report, parent company financial statements, SECR coverage, Companies House identifiers are all included in UKSEF, so the same document carries UK-specific digital reporting alongside the financial statements.
Tag once, satisfy both regulators:
The taxonomy includes the identifiers Companies House needs, so a single report serves both the FCA’s NSM and Companies House without rework.
Cut the workload after year one:
Tagging decisions roll forward from one annual cycle to the next, so subsequent filings take a fraction of the first year’s effort.
License or outsource:
Use Seahorse with your in-house team, or work with a certified UK partner who delivers tagging as a managed service on the same platform.
Want to see how Seahorse fits your filing setup? Get in touch to walk through Seahorse with your reporting team or for an introduction to a certified UK tagging partner.