FRC iXBRL 2026 Update: 5 Tagging Errors the Regulator Is Still Finding in UK Filings
What the FRC’s Latest Structured Digital Reporting Review Means for Your iXBRL Submission
TLDR: The FRC reviewed 30 UK listed companies and found five iXBRL tagging errors appearing consistently across the market. None of them triggers a gateway rejection. All of them sit on the public record. DataTracks catches every one before submission.
On May 20, 2026, the Financial Reporting Council published its latest review of structured digital reporting, identifying areas where relatively simple improvements would significantly enhance the quality, consistency and usability of digital financial reporting.
The FRC reviewed 30 UK listed companies’ 2024/25 annual reports. The verdict: most files are well structured and comply with requirements, but the FRC continues to identify areas where basic checks would address quality issues, alongside more judgmental areas.
These are not exotic edge cases. They are the same five errors appearing across the same market, year after year. And they all share one characteristic: none of them triggers a gateway rejection. They pass submission. They sit on the public record. And they are wrong.
This blog covers exactly what the FRC found, why these errors matter more in 2026 than they ever have, and what it means for any UK company or accounting firm submitting iXBRL-tagged accounts.
For a foundational guide to iXBRL requirements, read our iXBRL tagging for HMRC guide first.
Why the FRC Review Matters More in 2026
Since 2021, certain companies admitted to trading on UK regulated markets such as the London Stock Exchange have been required to produce their annual financial report in a structured digital format using iXBRL under FCA rules enabling that information to be machine-readable.
But the landscape has shifted significantly. High-quality structured data plays an important role in UK capital markets, particularly as data-driven analysis and artificial intelligence tools become more widely used to inform investment decisions.
The data inside your iXBRL file is no longer just a compliance box to tick. It is being consumed by AI tools, institutional investors and analytical platforms. An error that passed the gateway undetected in 2022 matters far more in 2026 when that data feeds directly into automated analysis.
Companies with significant tagging issues may receive direct communication from the FRC. That is a significant escalation from the previous position and a clear signal that the regulator is moving toward active enforcement rather than passive observation.
The 5 iXBRL Errors the FRC Found in 2026
Error 1: Inconsistent Level of Tagging
Disclosures that cover multiple accounting topics are often not fully tagged. Companies frequently apply only a single, high level tag where more detailed or multiple tags are required, reducing consistency and comparability across filings.
This is the most widespread error in the FRC’s review. A company disclosure that covers both revenue recognition and segment reporting, for example, should carry tags for both concepts. Applying a single umbrella tag satisfies the format check at the gateway but leaves the underlying data incomplete and non-comparable across the market.
The FRC notes that the FCA provides a list of mandatory tags that filers can use to support their review and recommends that policies and disclosures relating to significant and material items are fully tagged.
Error 2: Tags Chosen by Label Rather Than Accounting Meaning
Common pitfalls include misapplication of tags from irrelevant accounting standards. The FRC’s review found that tags are sometimes selected based on how a label reads rather than the underlying accounting concept. This results in identical figures being tagged inconsistently within the same report.
The correct approach is to choose tags by accounting definition and context, ensure each tag applies consistently to all instances of the same concept throughout the report, and review repeated figures to confirm alignment. Our guide on what the HMRC gateway does and does not check covers this in detail. The gateway accepts the format, not the conceptual accuracy.
Your iXBRL passed the gateway. The FRC says that is not enough.
Five errors survive submission and still end up on your public record. DataTracks pre-validates every file against the 2026 FRC taxonomy before it reaches the gateway. From £50.
Error 3: Overuse of Custom Extensions
Inappropriate use of custom tags and extensions being created when not necessary continues to be flagged. Custom extensions fragment comparable information across the market because they cannot be mapped against standard taxonomy concepts by analytical tools.
The FRC noted inconsistencies in anchoring where narrower extension elements are not being anchored to the wider base taxonomy element, or the type attribute value of an extension concept often does not reflect the type of information marked up in the iXBRL document.
The FRC’s position is clear: standard tags should be used wherever an appropriate element exists. Extensions should only be used where a disclosure genuinely cannot be represented using existing taxonomy concepts, with a documented rationale.
Error 4: Weak Anchoring of Extensions
Where extensions are used, proper anchoring of extension taxonomy elements is critical for linking meaningful additional information to the line item being tagged. Inaccurate anchoring can make it difficult for users to analyse the information as it is unclear what IFRS item it should be compared against across a peer group.
The FRC found anchors that are overly broad or conceptually imprecise. For example, an item from the Statement of Comprehensive Income being anchored to a Statement of Financial Position concept. Anchoring decisions should be guided by accounting meaning rather than technical convenience.
Error 5: EPS Scaling Errors
EPS continues to be one of the most common sources of error, typically caused by incorrect scaling. For example, £45 rather than 45 pence.
The FRC notes that EPS scaling errors are often not immediately apparent, which is precisely what makes them so dangerous. A figure that looks plausible in isolation could be technically wrong by a factor of 100. The regulator recommends a detailed review of the data that the tagging produces specifically to identify these errors before submission.
The 5 FRC iXBRL Errors at a Glance
Error | What goes wrong | Caught by HMRC gateway | FRC recommendation |
1. Inconsistent tagging depth | Single high-level tag applied where multiple detailed tags are required | No | Fully tag all policies and disclosures relating to material items |
2. Tags by label not meaning | Tag selected based on label wording not accounting concept | No | Choose tags by accounting definition and apply consistently throughout |
3. Overuse of custom extensions | Bespoke extensions created where standard taxonomy tags exist | No | Prioritise standard tags. Use extensions only with documented rationale |
4. Weak anchoring | Extensions anchored to generic or wrong concepts | No | Guide anchoring decisions by accounting meaning not technical convenience |
5. EPS scaling errors | £45 entered where 45 pence is correct value | No | Conduct detailed data review of all EPS figures before submission |
The FRC reviewed 30 companies. All five errors were still there. Is yours one of them?
You filed. The gateway accepted it. But did anyone check whether your EPS figures are scaled correctly, your tags map to the right accounting concepts and your extensions are properly anchored? DataTracks does. Before submission. From £50.
Three Additional Issues the FRC Flagged
Beyond the five core tagging errors, the FRC’s 2026 review identified three process failures that are creating additional compliance risk.
Validation warnings not investigated
Validation errors and warnings identified during preparation or filing are not always fully investigated or resolved. Ignoring warnings can indicate underlying data quality issues and reduces confidence in the structured data. The FRC recommends that companies ensure that sufficient time exists in the process to follow up any issues with their vendor or tagging agent.
Filing not confirmed on the NSM
A proportion of companies continue to file late or fail to ensure that their structured report is successfully published on the National Storage Mechanism. The FRC recommends that companies build into their process a post-submission check of the FCA’s NSM website to confirm their filing has been published and is displaying as expected.
iXBRL report not available on company website
The FRC noted that placing a copy of the iXBRL report on a filer’s website, preferably with a viewer, is good practice but that some companies are failing to do this. FRC research in 2023 indicated that institutional investors were accessing iXBRL reports via filers’ websites. AI tools also increasingly rely on the XHTML version of reports.
FRC 2026 iXBRL Compliance Checklist
| Requirement | Action required | Risk if missed |
| Full tagging of material disclosures | Tag all policies and disclosures covering material items at detailed level | Non-comparable data. Potential FRC communication. |
| Tags chosen by accounting meaning | Review every tag against the accounting concept it represents | Inconsistent figures across same report |
| Custom extensions minimised | Challenge every extension against the standard taxonomy first | Fragmented data. AI tools cannot map to peer group. |
| Extensions correctly anchored | Anchor to the correct base taxonomy element by accounting meaning | Unusable extension data. FRC review flag. |
| EPS figures reviewed for scaling | Run a dedicated check on all EPS data after tagging | Material scaling error on public record |
| Validation warnings resolved | Build time into process to investigate and resolve all warnings | FRC will treat unresolved warnings as quality issues |
| NSM publication confirmed | Check the FCA NSM after submission to confirm publication | Filing treated as incomplete |
| iXBRL report on website | Publish with viewer in investor section of website | Reduced investor access. AI tools cannot use the data. |
What This Means for Non-Listed Companies and CT600 Filers
The FRC’s 2026 review focuses on listed companies filing under FCA Disclosure and Transparency Rules. But the iXBRL errors it identifies are not unique to listed company filings. They appear in CT600 submissions too.
HMRC has required iXBRL-tagged accounts and computations with every CT600 since 2011. The HMRC gateway validates format, not conceptual accuracy. Tags selected by label rather than accounting meaning, custom extensions used unnecessarily, EPS scaling errors and weak anchoring all pass through the HMRC gateway without being flagged.
HMRC’s own systems analyse the tagged data after acceptance. A CT600 filing with EPS scaling errors or wrong taxonomy concepts is not rejected. It is accepted and recorded, with the error sitting on the company’s HMRC record until an enquiry opens or an amendment is required.
The FRC’s 2026 review is written for listed companies. But every accountant and tax manager filing CT600 returns should read it as a checklist for their own submissions. Our CT600 filing guide covers the specific HMRC taxonomy requirements in full.
The 2026 UK Taxonomy Suite: What Changed
The Financial Reporting Council has released the 2026 UK Taxonomy Suite, marking the latest update in digital reporting infrastructure for the UK and Ireland. The release includes updates to the FRC Taxonomy Suite, Charities Taxonomy and Irish Taxonomy alongside supporting documentation, mapping files and presentation sheets highlighting key changes.
Notable additions enable compliance with the UK Endorsement Board’s IFRS 7 amendments and support Financial Reporting Exposure Draft FRED 85. Enhanced disaggregation options for revenue, improved audit disclosure concepts and updated Statements of Recommended Practice dimensions also feature prominently.
Using an outdated taxonomy version is exactly the type of error that becomes more likely when taxonomy updates are not tracked. The FRC encourages use of the latest or penultimate taxonomy versions for filings. DataTracks automatically applies the current taxonomy version to every submission.
What DataTracks Catches That the Gateway Does Not
Every one of the five errors in the FRC’s 2026 review is caught by DataTracks pre-validation before the file reaches the gateway or the NSM.
| FRC 2026 Error | HMRC/FCA gateway catches it | DataTracks pre-validation catches it |
| Inconsistent tagging depth | No | Yes |
| Tags by label not accounting meaning | No | Yes |
| Custom extensions where standard tags exist | No | Yes |
| Weak or imprecise anchoring | No | Yes |
| EPS scaling errors | No | Yes |
| Outdated taxonomy version | Partial | Yes, always current taxonomy |
| Validation warnings unresolved | No | Yes, all warnings reviewed before submission |
DataTracks was the first HMRC-recognised iXBRL provider in the UK. Every file we submit is checked against the current FRC taxonomy, validated for conceptual accuracy and reviewed for EPS and scaling errors before it goes anywhere near the submission gateway.
The FRC is watching. Is your iXBRL clean enough to survive the scrutiny?
Companies with significant tagging issues may now receive direct communication from the FRC. DataTracks pre-validates every file against the 2026 FRC taxonomy and catches every error the regulator flagged. First HMRC-recognised iXBRL provider. From £50.
Frequently Asked Questions
What did the FRC's 2026 structured digital reporting review find?
The FRC’s report draws on a detailed review of 30 UK listed companies’ 2024/25 annual reports alongside broader market analysis. The five main errors are inconsistent tagging depth, tags chosen by label not meaning, overuse of custom extensions, weak anchoring and EPS scaling errors. Source: FRC Structured Digital Reporting: Insights 2025/26.
Does the FRC review apply to CT600 filings as well as listed company reports?
The FRC’s review focuses on listed companies filing under FCA DTRs. However, the same tagging errors occur in CT600 submissions to HMRC. The HMRC gateway accepts format, not conceptual accuracy, meaning the same errors that the FRC identifies in NSM filings can sit on a company’s HMRC record undetected.
What is an EPS scaling error in iXBRL?
EPS scaling errors are typically caused by incorrect scaling. For example, £45 rather than 45 pence. The error passes gateway validation because the format is correct, but the value is wrong by a factor of 100. DataTracks conducts a dedicated EPS scaling check on every file before submission.
What is the 2026 UK Taxonomy Suite?
The FRC has released the 2026 UK Taxonomy Suite marking the latest update in digital reporting infrastructure for the UK and Ireland. The release enables compliance with the UK Endorsement Board’s IFRS 7 amendments and supports Financial Reporting Exposure Draft FRED 85. DataTracks applies the current taxonomy version to every submission automatically.
Can the FRC contact companies directly about iXBRL errors?
Yes. Companies with significant tagging issues may receive direct communication from the FRC. This represents an escalation from previous years and signals that the regulator is moving toward active enforcement on tagging quality.
How does DataTracks catch these errors before submission?
DataTracks pre-validates every iXBRL file against the current FRC taxonomy before submission. This includes conceptual accuracy checks, EPS and scaling reviews, extension validation, anchoring verification and taxonomy version confirmation. None of which are performed by the HMRC gateway or the FCA NSM at submission.
