The name I wanted CarCo is already taken, if I change it slightly to CarCo hire to get the company registered at companies house can I then only use the CarCo bit on my advertising, signage, clothing, email, website etc ? Thanks
Companies House will let you know if they think the name is too similar to an existing name.
If the name is similar to and you are in a similar type of business as an existing company, that company is bound to object especially if you use THEIR name as your logo.