All company registration numbers (CRNs) have 8 characters - some are all numbers, whilst others contain letters and numbers. These numbers vary depending on the issuing registrar, of which there are three - Companies House Cardiff (English and Welsh companies); Companies House Edinburgh (Scottish companies); and Companies House Belfast (N.Irish companies).
The variations are as follows:
Limited companies in England and Wales: eight numbers long, beginning with 0
Limited companies in Scotland: SC followed by six numbers
Limited companies in N. Ireland: NI or RO followed by six number
LLPs in England and Wales: OC followed by six numbers
LLPs in Scotland: SC followed by six number
LLPs in Northern Ireland: NC followed by six numbers
There are the most common variations you will come across on the Companies House register. The slight differences in prefixes makes it easier to identify the country of registration and legal structure of the business.