What is a CRN number? | 2026/27 UK Business Guide

If you are setting up or managing a limited company in the UK, you will frequently encounter the term CRN. To accurately answer what is a CRN number, practitioners must evaluate both corporate law and tax compliance. A Company Registration Number (CRN) serves as the unique identifier for your business entity, acting as its corporate fingerprint from the moment of incorporation until dissolution.

For the 2026/27 tax and legal year, understanding your CRN is crucial due to the new identity verification rules introduced by the Economic Crime and Corporate Transparency Act 2023 (ECCTA 2023), which introduces new identifiers that you must not confuse with the CRN.

The Legal Definition of a CRN

The Companies Act 2006 (CA 2006) provides the strict statutory foundation for the CRN. Under section 1066(1) of CA 2006, the Registrar of Companies must allocate a number to every company upon incorporation, which becomes legally known as the “company’s registered number”.

This number is permanently tied to the corporate entity. HMRC guidance confirms that a CRN is unique and cannot change, even if the company subsequently changes its registered name or its registered office address.

CRN Format and Length

Section 1066(2) of CA 2006 states that the CRN consists of one or more sequences of figures or letters, as determined by the registrar.

In practice, Companies House issues CRNs in a highly specific format. A CRN is up to eight characters long.  It typically consists of either eight numerals or a two-character alphabetical prefix followed by up to six alphanumeric characters.

Common prefixes denote the company’s jurisdiction or entity type:

• Standard English and Welsh companies generally receive an 8-digit numeric CRN.
• Scottish companies receive an “SC” prefix.
• Northern Irish companies receive an “NI” prefix.
• Limited Liability Partnerships (LLPs) receive an “OC” or “SO” prefix.

Statutory Disclosure Requirements

You must display your CRN publicly on official company materials. Section 1066(5) of CA 2006 directly references the trading disclosure requirements imposed by regulations under section 82 and section 1051.

These regulations mandate that a company must prominently disclose its CRN on all forms of business correspondence, order forms, and its company websites. Failure to properly display the CRN breaches the trading disclosure rules and can result in financial penalties for both the company and its acting directors.

Tax Importance: Data Matching in COTAX

Beyond Companies House, the CRN plays a critical role in your company’s tax compliance. HMRC uses the CRN as the primary data matching tool to link Companies House data with its own Corporation Tax computer system (COTAX).

When you incorporate a new company (identifiable by status codes such as ‘C’ for Limited Company/PLC or ‘E’ for Close Investment Holding Company), the automatic data feed from Companies House sends the CRN to HMRC, which uses it to automatically set up the new COTAX record.  HMRC mandates that its officers maintain accurate CRNs on these records to ensure accurate risk assessment and to process tax amendments correctly.

CRN vs UTR (Unique Taxpayer Reference)

New directors frequently confuse the CRN with the UTR. You must distinguish clearly between the two identifiers:

• CRN: Assigned by Companies House upon incorporation to identify the legal entity on the public register.
• UTR: Issued by HMRC specifically for tax purposes.

When Companies House notifies HMRC of your new CRN, HMRC uses that CRN to set up the COTAX record and subsequently issues a 10-digit UTR to the company, typically via form CT41G.  When you notify HMRC of the start of your first accounting period, or when you submit your annual Corporation Tax Return (CT600), you must provide both the CRN and the UTR.

2026/27 Context: CRNs vs UIDs (ECCTA 2023)

For the 2026/27 period, the Economic Crime and Corporate Transparency Act 2023 (ECCTA) has introduced a new layer of identification that practitioners must manage.

While the CRN identifies the company, the newly inserted section 1082 of CA 2006 now grants the Secretary of State the power to allocate “unique identifiers” (UIDs) to individuals.  This applies to individuals acting as directors, secretaries, or verified individuals interacting with Companies House.  You must ensure you do not confuse the entity-level CRN with the new individual-level UIDs when filing documents under the updated ECCTA verification framework.

Summary of CRN Rules (2026/27)

Next steps for research: Review the specific trading disclosure requirements under The Company, Limited Liability Partnership and Business (Names and Trading Disclosures) Regulations 2015 to verify the exact locations and formats where the CRN must be displayed on digital and physical communications.