Playing on American servers is always going to give you a high ping due to the distance involved but you should be able to get lower pings on UK servers. I usually get 30-50ms.

How are you connecting to the router? If it is wireless then make sure the signal is strong and try temporarily connecting by a cable and see if it makes any difference.

Pings will also be increased if anyone else is using the bandwidth for anything else so check to see whether other people are downloading anything or streaming music etc. If anyone uses a P2P app (such as Limewire) then this will considerably increase your ping as it eats away your bandwidth. Remember to make sure your router has a network key if it's wireless in case any neighbours are using your connection.

Also be aware that sometimes a high ping is caused by a lack of bandwidth at the server's end in which case there is nothing you can do about it other than to move onto a different server. A good indication that this might be happening is if all players on the server have a ping > 100ms.