How to register a trading as name:
Trading as names do not have to be registered anywhere.
The best protection for a "trading as" name is to apply to register a trademark. A trademark gives strong legal protection against anybody else copying your name that trades in the same industry.
However it is best practice to tell your bank as they may not accept cheques and other payments made out to the trading style rather than the main limited company if you don’t.
While you do not have to register your trading as name anywhere a lot of people do choose to register it as a company which they then keep dormant. By registering the trading as name as a company it means no-one else can register a company with that name or with one that is similar. It also helps to establish your right to that name if there is ever a dispute about it.
Checking trading as names
Before deciding on a trading as name you should run all of the same checks on the name that you would with any other company registration, This is to make sure no-one else is already using that name, or has established it as their intellectual property.