The company authentication code was introduced by Companies House to ensure that any instructions it received about making changes to a company had been given by authorised persons in the limited company.
In the past, forms such as Form 287 (change of registered office) were sent to Companies House by bogus individuals. On the assumption that the documents were genuine, the requested changes were then made and enabled persons who were not officially representatives of the company to commit fraud or other illegal acts.
Authentication codes are now issued with every UK company formation. The use of authentication codes and initial registration with the Companies House Proof Scheme must now take place online. As the person incorporating the company would be provided with the unique code, there is generally less chance of false registrations taking place. When making any changes to the limited company, the authentication code must be given and validated.
It is possible to change your authentication code online to something that is easier to remember. In this case, the original code must still be used in order to log on to the system to make the alteration.
Please note that the authentication code can only be used for online filing.