What is a company registration number?

When a limited company is formed in the UK, it is assigned a unique identifier by Companies House. This number appears on the certificate of incorporation and is required in a range of business and legal contexts. Many founders use it without fully understanding what it is, where it appears, and why it matters beyond simply being a reference number.

A company registration number — also referred to as a CRN — is a unique number assigned by Companies House at the point of incorporation. It identifies the company on the public register and remains fixed for the life of the company, even if the name changes. The CRN is required on all official company correspondence, including invoices, letters, and the company website. It is also used when filing documents with Companies House and corresponding with HMRC about Corporation Tax.

The CRN is distinct from the company's Unique Taxpayer Reference, assigned by HMRC for tax purposes, and from any VAT registration number. Confusing these identifiers is a common source of administrative errors, particularly for founders new to running a limited company. Our guide to company registration and compliance for UK founders explains each identifier and where it is required.