Most wireless devices are rated to 100m indoor range nd 400m outdoor range, this gives plenty of room to play with. Also as far as gaming & internet is concerned, do remember that broadband does not even come close to even the lowest bandwidth available over ethernet conections, so even if it were supurbly poor at 1mb link, you'd be fine.
Some recommendations:
D-Link DWL-G810
Netgear WGE111
or for a slightly more unconventional solution:
Netgear XE102
I couldn't find a product located in the UK, but I know there are a couple of simular ones out there. With this unit you can create a network via wiring in your electrical sockets. It only has a maximum speed of 14Mbs but that's plenty for internet and gaming, however I'm really not sure what the limit is in regards to distance between wiring sockets, this is also assuming all the sockets in your flat or whatever share the same electrical path.