In our day jobs we often meet prospective new clients who have registered the name of their new start up company at Companies House and have then commenced a programme of advertising to jump start their business. Although checking, via Companies House, that your company name has not already been taken is obviously important it should be borne in mind that availability of a name at Companies House does not necessarily mean you are free to use that name in the course of business. Neither does registration of a company name at Companies House provide the right to prevent others from trading under the same name.
Prior to adopting a new name, it is therefore prudent to speak to a trade mark attorney to ensure that the name is free for adoption and, further, to ensure that you put in place the best form of protection to enable you to prevent others from using a similar name in future.
Further information can be found here.