Are you talking about pounds you have in a bank account, or do you physically have them with you?
If they are in a bank account, there are many free* services that can do this for you. I use
http://www.xetrade.com but others can tell you about other services. I used them last week to send some dollars home: they do EFT (in the US) and BACS transfer (in the UK) for free.
If you have cash, and it's a couple of hundred or less, maybe we can make a deal: I'm going to the UK next month, and will need some pounds. I'd be happy to swap them with you for the prevailing exchange rate (this would benefit both of us, see below).
*free: all currency conversion services make a profit somewhere. The two ways they do this are by charging a percentage commission, or by using a 'spread'. A spread is where they give different rates converting between currencies in different directions: go pounds->dollars->pounds and you'll end up with less money than you started with. They pocket the difference.
Hope this helps.
chwboy