There are various UK distributors of video games in the UK, but you will find very few stock all platforms so you’ll most probably have to register with all of them. Heres just a few:
http://www.kochmedia.co.uk – Distributors of Nintendo products predominantly. Computer software and games in stock too.
http://www.centresoft.co.uk – Distributors of Sony PS1, PS2, PSP, and PS3. They also have UMD movies and Blu-Ray’s. If I remember correctly, they also stock budget PC titles but I’m not too sure.
http://www.gem.co.uk – They have the distribution rights of Xbox and Xbox 360 games. As well as having exclusive distribution rights over a number of publishers (Take Two is one of them, so ideal for GTA stock). They’ve loads of other products, too, such as MP3 players and gaming accessories.
You should know none of the above will deal with eBay sellers. So do not mention it, if that’s where you plan to sell. Get a basic store live (Pete would be the person to talk to) and say this is where you’ll be selling your games. It should suffice.
As for being a “registered business”, that’s a legal requirement anyway and carries serious consequences if you choose to try and slip under the radar. Its tax evasion at the end of the day, and it can result in a prison sentence! Many do try and get away with it (there’ll get caught sooner or later), but its best to do things by the book from day 1. No nasty surprises that way!