Companies House Number Data Matching: The Best Key for UK B2B Data

If you hold UK company data in more than one system, the company registration number (CRN) is the one field that lets every record agree. Names change, websites change and groups trade under several brands, but the number Companies House issues stays with the legal entity. This guide explains why Companies House number data matching beats name matching, what the identity verification deadline of 18 November 2026 means, and a practical recipe for attaching the number to your records.

Why is the company registration number the best key for UK B2B data?

A good key has three properties: it is unique, it does not change, and anyone can look it up. The CRN has all three.

• Unique and permanent. HMRC's own manual puts it plainly: "CRNs are unique and cannot change even if a company changes its name or Registered Office address".¹ The number is issued when the company is formed and appears on the certificate of incorporation, which "confirms the company legally exists and shows the company number and date of formation".²
• Free to look up. Companies House describes its API as providing "access to all of the public data we hold on companies free of charge".³
• Structured. A CRN is either up to eight numerals, or normally two letters (the prefix) followed by up to six characters.¹ That makes it easy to validate before you store it.

Compare the alternatives. A company name can be changed by a resolution. A domain can be sold, redirected or shared by several group companies. A registered office moves when the accountant changes. None of that affects the CRN, so it is the field to join on when you merge a CRM, a billing system and a list of identified website visitors.

One caution: the CRN identifies a legal entity, not a commercial relationship. A group with ten subsidiaries has ten numbers. That is a feature, because it lets you decide deliberately whether to roll activity up to the group or keep each entity separate.

What happens on 18 November 2026?

Identity verification became a legal requirement at Companies House on 18 November 2025, under the Economic Crime and Corporate Transparency Act 2023.⁴ Companies House announced that existing directors would confirm their verification "at the same time as they file their next annual confirmation statement, during a 12-month transition period", and estimated that 6 to 7 million people would need to verify "by mid-November 2026".⁵ Its annual report for 2025 to 2026 refers to "the end of the transition year (November 2026)".⁶ Twelve months from the start date is 18 November 2026, which is the date most commentators use for the end of the transition.

If you are reading this before 18 November 2026, two points matter more than the headline date:

1. Most individual deadlines fall earlier. A director provides their personal code "as part of your company's next confirmation statement". A person with significant control (PSC) who is not a director "must provide your personal code within the first 14 days of your birth month".⁷ For many people, the due date has already passed or falls before 18 November 2026.
2. Unverified directors block filings. GOV.UK guidance says a company "will be unable to file its confirmation statement unless all its directors are verified".⁸

Not complying on time is an offence, and the government's campaign site says the consequences include "a financial penalty".⁴ We have not found a specific penalty amount on GOV.UK, so check the official guidance rather than figures quoted elsewhere. Progress has been substantial: by 31 March 2026, Companies House reported 3 million verifications through GOV.UK One Login and 783,000 through Authorised Corporate Service Providers.⁶ This is general information, not legal advice.

Why does this belong in a data article? Because verification ties checked people to company records, the register becomes a more reliable reference point, and that makes it an even better anchor for your own data.

How does this relate to visitor identification?

Website visitor identification works out which organisation is behind a visit from its IP address and network data. The raw output is usually a network owner's name, a domain, or a brand. Those are useful, but they are not a legal entity.

An identified visit becomes far more useful once it resolves to a CRN:

• Trading names collapse. "Acme Fixings", "Acme Group" and "ACME FIXINGS LIMITED" become one record.
• Group structures become explicit. You can see that two visits came from different subsidiaries of the same parent.
• CRM duplicates stop multiplying. When the visit is pushed to your CRM, it can join an existing account instead of creating a new one.

If you want the mechanics of the first step, our explainer on how an IP address becomes a company name covers it. The principle for the second step is simple: store the number alongside the match, and keep the match's confidence alongside both. Scout, for example, gives every identified company a confidence score from 1 to 99 with a one-line reason, because no IP match is certain.

What does the free Companies House API give you?

The Public Data API covers the core register. The endpoints you will use most are:

These paths come from the API reference.⁹ The company profile includes the name, number, status, SIC codes, registered office, previous names, company type and date of creation.¹⁰ Previous names matter for matching: they are how you connect an old CRM record to today's entity.

The rate limit is generous for enrichment but not for bulk work: "You can make up to 600 requests within a five-minute period", after which you receive 429 Too Many Requests for the rest of the window.¹¹ For whole-register jobs, Companies House publishes a free monthly snapshot of live companies, updated "within 5 working days of the previous month end".¹²

A matching recipe, in plain language

This is a generic approach that works for CRM clean-ups, list imports and identified visitors alike.

1. Normalise the name. Lower-case it, strip punctuation, and standardise suffixes (ltd, limited, plc, llp). Keep the original too.
2. Search for candidates. Call /search/companies with the normalised name, or /advanced-search/companies with company_name_includes, company_status and location when you know roughly where the company is.¹³
3. Disambiguate. Score each candidate on name similarity, then use a second signal: postcode or town from your record, SIC code against the industry you expect, and status (prefer active). A domain on your record can be compared with the company name, but treat that as weak evidence.
4. Check previous names. Fetch the profile of the top candidates and compare against previous company names.¹⁰
5. Store the CRN, the match method and a confidence. An exact name and postcode match deserves more trust than a fuzzy name alone.
6. Leave it blank when unsure. A missing number is honest. A wrong number silently merges two companies.

At 600 requests per five minutes, a search plus two profile checks per record handles roughly 200 records per window, so plan larger jobs around the bulk snapshot.

Where does matching fail?

Some records will not resolve cleanly, and your confidence should fall with them.

• Trading names. A brand may not appear in the company's registered name at all.
• Dormant lookalikes. Similar names can belong to dormant or unrelated companies. Status and filing history help separate them.
• Overseas entities. A foreign parent with a UK branch may not have the UK company you expect.
• LLPs versus limited companies. A firm may trade as an LLP while a similarly named limited company exists alongside it. Check the company type on the profile.
• Dissolved companies. The number stays unique, but the company behind it may no longer exist. In the quarter from April to June 2026, 156,515 companies were struck off and dissolved.¹⁴
• Businesses without a number. Sole traders can start trading without registering a company;¹⁵ there is no CRN to find.

For scale, there were 5,516,377 companies on the register at the end of June 2026.¹⁴ That count moves every month, so check the latest release before quoting it.

Make the number part of every record

Treat the CRN as the primary key for UK companies, keep names and domains as attributes, and keep a confidence on every link between them. Visitor identification data is most useful when it follows the same rule. For the wider picture, read our guide to website visitor identification or see which plan fits your traffic.

Scout resolves visits to companies, then tells you how sure it is. Start a 14-day free trial, no card needed.

Frequently asked questions

Is Companies House data free to use commercially?

Companies House says its API provides access to all of the public data it holds on companies free of charge, and its monthly company data snapshot is also free. GOV.UK reminds users they are responsible for complying with data protection, copyright and other legislation. Officer and PSC records name real people, so UK GDPR applies if you store or use them.

Do sole traders have a company number?

No. A sole trader is not a company, and GOV.UK explains that sole traders can start trading without registering a company. Limited companies are issued a number when they are formed, and it appears on the certificate of incorporation.

How many companies are on the register?

Companies House statistics show 5,516,377 companies on the register at the end of June 2026. The figure changes every month as companies are incorporated and dissolved, so check the latest quarterly release before you quote it.

Does a company number ever change or get reused?

HMRC guidance says CRNs are unique and cannot change even if a company changes its name or registered office address. Because numbers are unique, a match to a dissolved company still points to one specific entity, so check its status before you rely on it.

Is 18 November 2026 my personal deadline for identity verification?

Probably not. Existing directors provide their personal code with the company's next confirmation statement, and PSCs who are not directors do so in the first 14 days of their birth month, so many deadlines fall earlier. This is general information, not legal advice; check GOV.UK guidance for your situation.

Sources

1. GOV.UK (HMRC internal manual): COM40011 Company registration numbers gov.uk
2. GOV.UK: Set up a private limited company, register your company gov.uk
3. API Catalogue (api.gov.uk): Companies House API api.gov.uk
4. Changes to UK company law (GOV.UK campaign): Identity verification changestoukcompanylaw.campaign.gov.uk
5. GOV.UK: Companies House confirms identity verification rollout from 18 November 2025 gov.uk
6. GOV.UK: Companies House annual report and accounts 2025 to 2026 gov.uk
7. GOV.UK: When you need to verify your identity for Companies House gov.uk
8. GOV.UK: Verifying your identity for Companies House gov.uk
9. Companies House: Public Data API specification summary developer-specs.company-information.service.gov.uk
10. Companies House: Public Data API, company profile developer-specs.company-information.service.gov.uk
11. Companies House: Developer guide, rate limiting developer-specs.company-information.service.gov.uk
12. Companies House: Free Company Data Product download.companieshouse.gov.uk
13. Companies House: Public Data API, advanced company search developer-specs.company-information.service.gov.uk
14. GOV.UK: Incorporated companies in the UK, April to June 2026 gov.uk
15. GOV.UK: Business legal structures gov.uk