A regex to check UK Company numbers - ie the reference assigned to companies in the UK via Companies House

UK Company Number regex

/^((AC|ZC|FC|GE|LP|OC|SE|SA|SZ|SF|GS|SL|SO|SC|ES|NA|NZ|NF|GN|NL|NC|R0|NI|EN|\d{2}|SG|FE)\d{5}(\d|C|R))|((RS|SO)\d{3}(\d{3}|\d{2}[WSRCZF]|\d(FI|RS|SA|IP|US|EN|AS)|CUS))|((NI|SL)\d{5}[\dA])|(OC(([\dP]{5}[CWERTB])|([\dP]{4}(OC|CU))))$/

I've written this page with a list of the meanings of the various prefixes: https://chguide.co.uk/general/company-number.html . I have also found a quite comprehensive list in some old docs:

This page has description for PC prefix, but the provided regex does not include it.
In addition, in the official documentation SI prefix listed in the section with prefixes for companies with no available data (only name is available).

Had another go at it:

/^(((AC|CE|CS|FC|FE|GE|GS|IC|LP|NC|NF|NI|NL|NO|NP|OC|OE|PC|R0|RC|SA|SC|SE|SF|SG|SI|SL|SO|SR|SZ|ZC|\d{2})\d{6})|((IP|SP|RS)[A-Z\d]{6})|(SL\d{5}[\dA]))$/;

The rules around registered societies (starting with IP|SP|RS prefix) could probably be tightened up, this is a more permissive regex, matches all the company numbers in the bulk CSV file.