Company Name Rules
You cannot incorporate a company using any name you like. Some names are prohibited (for example, those which suggest a connection with the Government or the Crown) and names will not be allowed if they are too similar to the names of existing companies. Guidance on restricted names can be seen here.
Companies House provides guidance on the rules for choosing names for new companies. Don't forget to check that the associated Internet domain name is available as well and it is always good advice to search for trade marks that might create difficulties if oyu intend to use the company name for tradign purposes.
Different rules entirely apply to the registration of domains on the Internet and the regulations also vary from country to country. For example, some countries will not allow the country's domain suffix to be registered to a domain unless there is an active trade mark and/or trading presence in the country. The best source of information on domain names is Nominet in the UK.