Hi I've just checked UK Forex, and the rate is 1.1427 to buy Euros. - it really is worth checking, and they are really helpful on the phone - the first time I called, I understood nothing! They also don't charge for doing the transfer.
Incidentally, to buy cash Euros at Link Exchange at Victoria station (for those in the UK going out to Spain) the rate is 1.1315 to buy Euros.
Paul (previous message) has given a really good explanation of how the exchange rate works. I'd like to add that if you want to see if you are getting a good rate, apart from looking at all the places where you can change, it's also helpful to look at the buying and selling rate - when they are close, you know that the broker is not making such a huge profit - whereas, for example, at the airport, the difference is very big, and they are raking it in!!Good luck Katy