palasojourner:without transfer fees and with the exchange rate as close as possible to the one of the Bank of England or the European Central Bank?
... but then how would the poor banks make an honest living? You should investigate which payment methods your particular fund will accept.and work around those. Generally speaking, if they use a bank for a draft or transfer they will get a highish charge (£10 - £20) and a reasonable exchange rate. If you use someone like auctionchex.com you will get a low charge and a poor exchange rate. A credit card might be ideal but not many funds accept this payment method.
The way to do what you want is to meet up with some trustworthy friend who is going on holiday. Years ago when I worked in Corfu I used to occasionally meet up with friends of friends to swap anything left from my small drachma salary for pounds at whatever happened to be the middle rate at the time. I did feel very guilty about depriving the banks of a living and, obviously, this is not something to consider undertaking with a dodgy bloke in a pub.