Analysis Report
An examination of Annual Financial Report submissions to the FCA's National Storage Mechanism
Under FCA requirements, the iXBRL annual report is the official report of record. According to the FRC's 2023 institutional investor survey, more than 30% of investors are already using XBRL reports for analysis. As AI-driven analysis becomes more prevalent, the quality and availability of structured data becomes increasingly critical for market efficiency and investor protection.
Key facts about the UK's digital reporting regime.
| Mandatory Since | Financial years beginning on or after 1 January 2021 |
| UK Filers | Approximately 930 listed companies |
| Governing Regulation | DTR 4.1.14R-4.1.15R and the onshored ESEF RTS |
| Required Format | XHTML with Inline XBRL tagging for consolidated IFRS financial statements |
| Filing Location | National Storage Mechanism (NSM) |
The FRC's Structured Digital Reporting 2024/25 Insights (April 2025) examined 25 annual reports and identified quality issues including unnecessary custom extensions (~14% of FTSE 100 tags), poor anchoring, incorrect tag semantics, and missing mandatory tags. The FRC has since launched a public UK iXBRL viewer and is using their CODEx project tools for market-wide analysis. This analysis complements that work by examining the broader population of NSM submissions.
All XHTML and HTML files submitted to the NSM during the analysis period, classified by content type and data extractability.
| Category | Count | Percentage | Data Extractable? |
|---|---|---|---|
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1 ESEF iXBRL Package: Complete ESEF-compliant submission with taxonomy package and machine-readable financial data conforming to DTR 4.1.14R requirements.
2 Standalone iXBRL: Native iXBRL file with extractable XBRL facts but submitted without the full ESEF taxonomy package structure.
3 PDF Conversion: A PDF document converted to HTML/XHTML format (typically via pdf2htmlEX). These preserve visual layout but contain no machine-readable structured data.
4 PDF-to-iXBRL: A PDF document converted to iXBRL format with embedded XBRL facts (typically via pdf2htmlEX with XBRL tagging). Contains extractable structured data but submitted without the full ESEF taxonomy package.
Note: This analysis excludes HTML announcements (RNS notices, press releases) which are not actual report filings.
When properly accounting for exempt entities (CIUs, debt issuers), operating companies subject to ESEF regulations have a 97.5% iXBRL compliance rate. The apparent "low" overall rate is because the NSM includes filings from entities legitimately exempt from ESEF requirements.
iXBRL adoption rates segmented by type of issuer and their regulatory status.
| Issuer Category | Filings | With iXBRL | Rate | ESEF Status |
|---|---|---|---|---|
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Collective Investment Undertakings (CIUs): Investment trusts, VCTs, and funds are explicitly excluded from ESEF under Article 1(3) of the UK-onshored Commission Delegated Regulation (EU) 2019/815.
Debt-only issuers: Companies with bonds but no equity shares listed are not required to prepare IFRS consolidated accounts or file iXBRL.
Foreign entities: Companies domiciled outside the UK may be subject to different regulatory regimes.
Based on files with valid iXBRL data.
Distribution of XBRL facts across compliant iXBRL submissions.
| Metric | Value |
|---|---|
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5 XBRL Facts: Individual tagged data points within an iXBRL document, including numeric values (ix:nonFraction) and textual disclosures (ix:nonNumeric).
6 Taxonomy: The classification schema used to categorise financial data. IFRS-full is the International Financial Reporting Standards taxonomy required for ESEF compliance.
Files grouped by whether structured financial data can be programmatically extracted.
| Status | Count | Percentage |
|---|---|---|
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View individual filings in the data explorer, or read our vision for how APIs and AI could transform the NSM into a world-leading financial data platform.
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