Check your PRA banking returns

Checks run, return by return

The Bank of England lists its validation rules for each return, and writes most of them into the taxonomy package as XBRL formulas. A return's active checks are those the Bank lists for it as XBRL rules, less any it or the package switches off. Line4 Check runs a check only once it is proven against Arelle 2.47.4, the open-source XBRL processor: on every test file of the return, the two give the same outcome and test it the same number of times, and Arelle tests it at least once.

Every report carries the same line, for example: “This free check runs 61 of the Bank of England's 61 active validation checks (100%) for its leverage ratio return (LVR001) on the banking taxonomy 4.1.1, every one proven against Arelle, the open-source XBRL processor, on 8 test files, plus 47 rules of the Bank's XBRL Filing Manual v1.0.1 in full and 2 in part. It is not a substitute for the validation run when you submit the return.”

What does not run, and why

646 of the Bank's 3,730 active checks for these returns do not run, counted return by return. Line4 Check never counts a check it does not run as passed. The reasons, each with the returns it applies to:

• Held back after differing from Arelle on test data: 74On at least one of Line4’s test files they did not give exactly the same result as Arelle, the open-source XBRL processor: a different outcome, or a different number of times tested. They stay out until the two agree.PRA001: 73 of its 1,441; RFB008: 1 of its 57
• Never evaluated by Arelle: 6Arelle did not evaluate them on any test file of the return, so there is nothing yet to prove them against. They stay out until a test file does.PRA001: 2 of its 1,441; PRA115: 3 of its 26; RFB008: 1 of its 57 (boe_b0281, boe_b0408, boe_b1033, boe_b1034, boe_b1035, boe_b1103_s)
• Not compiled, as no cell matches what they read: 552Each reads a value that matches no cell of the return’s templates, so Line4 could not compile them.PRA110: 552 of its 1,108
• Checks that use logarithms: 4Browsers and computers do not all compute logarithms to the same last digit, so the result could depend on the machine. Line4 Check leaves them out.PRA001: 2 of its 1,441; PRA116: 2 of its 531
• In the Bank’s list but missing from its package: 1The Bank’s list of validations says this check is in its XBRL for the return, but the Bank’s taxonomy package has no such check for it, so there is no formula to run.RFB004: 1 of its 162 (boe_v0830_m)
• On items no template of the return has: 9They read only concepts or members that none of the return’s templates has, so they can never apply to it. They are not counted as run.PRA001: 5 of its 1,441; PRA110: 2 of its 1,108; RFB008: 2 of its 57

The Bank's list of validations also has 188 rules for these returns that it does not write into its XBRL. They have no formula to run, in Line4 Check or in Arelle, and are not among the 3,730 above. Returns not built on the Bank's banking taxonomy are not checked here. Line4's library of the PRA's returns for banks gives the format of each.

How the proof works: the test files for each return are the Bank's own sample, test copies of it with facts changed, and synthetic returns built to fill its templates (24 samples, 19 test copies and 129 synthetic returns, 172 files in all). Arelle and Line4 run every check on every file, and a check runs here only when the two agree on all of them. Line4 Check is a prototype of the Line4 validation engine, not certified software.

The Bank's filing rules

The Bank's 4.1.1 release note asks firms to follow its XBRL Filing Manual (v1.0.1) for how the instance itself is written. Line4 Check checks 47 of its rules in full and 2 in part on every return, under the Bank's own numbers: the file name and encoding, the schemaRef and entry point, the filing indicators, the entity identifier, contexts and dates, units and decimals, nil and duplicate facts, and more. A broken MUST rule is an error and a broken SHOULD rule a warning, each shown in plain words first, then its number.

Checked in full, by the Bank's numbers: 1.1, 1.4, 1.5.(a), 1.6.(a), 1.6.(c), 1.6.1, 1.6.2, 1.6.3, 1.7.(b), 1.7.1, 1.13, 1.14, 1.15, 2.1, 2.2, 2.4, 2.6, 2.7.(a), 2.7.(b), 2.8.(a), 2.9, 2.10.(a), 2.10.(b), 2.11, 2.13, 2.14, 2.15, 2.16, 2.16.1, 2.17, 2.18.(a), 2.18, 2.19, 2.21, 2.22, 2.23, 2.24, 2.25, 2.26, 3.1.(a), 3.2.(a), 3.4, 3.5, 3.7, 3.9, 3.10 and 3.11.

Checked in part:

• Rule 1.5.(b), the schemaRef is checked against the module's entry point; the reference dates the Bank applies the entry point to are not (Line4 has them for the insurance frameworks only).
• Rule 1.9, XBRL 2.1, XML Schema and XBRL Dimensions validity as far as the reader sees it (contexts, units, numbers, dates, booleans, coded values, decimals, ids, datapoints of the module); not a full schema validation, and not the extensible enumeration lists, which the rule files do not carry.

Not checked:

• Rule 1.10, the codes and type of codes: the taxonomy's own validation rules check them.
• Rule 1.12, a complete report: an instance does not say what the firm should have reported.
• Rule 2.5, what the values mean: an instance does not say it.
• Rule 2.6.(a), meaning in ids: an instance does not say it.
• Rule 2.6.(b), the length of ids: the manual gives no measure.
• Rule 2.8.(b), the entity's registration with the Bank: an instance does not say it.
• Rule 2.18.(b), no rounding or truncation: the manual gives no measure.
• Rule 2.18.(c), a realistic accuracy: the manual gives no measure.
• Rule 3.1.(b), not checked yet: the engine does not compare an amount's unit with its Currency with significant liabilities (CUS) member.
• Rule 3.1.(c), not checked yet: the engine does not compare an amount's unit with its Currency with significant liabilities (CUS) member.
• Rule 3.2.(b), percentages as fractions: the manual gives no measure.
• Rule 3.3, what the values mean: an instance does not say it.
• Rule 3.8, the length of strings: the manual gives no measure.

Which taxonomy: 4.1.1

The Bank published the Bank of England Banking Taxonomy 4.1.1 with its release note of 27 August 2026, a corrective update that brings together 4.0.0 and 4.1.0. It implements three policy statements intended to take effect from 1 January 2027: Basel 3.1, the simpler capital regime for small domestic deposit takers, and the MREL reporting templates (release note). Firms that report own funds (PRA001 or PRA116) must adopt it. The 24 returns here are every entry point of the package, and a file names one in its schemaRef, such as http://www.bankofengland.co.uk/data/xbrl/fws/banking/leverage/2026-02-27/mod/lvr001.xsd. Line4 Check matches that address exactly, so a file is only ever checked against the rules of the return and release it names.

How it works

1. 01Your browser downloads the engine and the rulesThe Line4 engine with its XBRL-XML reader is compiled to WebAssembly (493 KB). Only the rules of the return you check are downloaded: the Bank’s leverage ratio rules are 23 KB, its own funds rules 3,575 KB. Your browser keeps them for next time.
2. 02Your file is opened on your computerThe XBRL-XML instance is read inside the browser tab, in a background worker so the page stays responsive. Its schemaRef says which return and taxonomy release it is. Nothing is uploaded.
3. 03The checks run and are listedEach failed check is listed by template, in plain words, with the value found, the value expected and the Bank’s rule code; broken filing rules come first, in a card of their own. Download it all as a CSV.

Questions