Company Registration Number (CRN) of the UK company as registered with
companies house. This is a unique code that Companies House uses to help
it quickly and correctly identify a company. A CRN is assigned upon
incorporation, which means that limited companies and LLPs (limited
liability partnerships) must have one.
Some other types of business do not require a CRN because they are not incorporated
and are not required to file their statutory records with Companies House.
Types of business not requiring a CRN include sole traders and general partnerships.
CRNs are always 8 characters long. These can be either 8 digits or 2 letters
followed by 6 digits.