Most banks will make a charge for converting the currency into an Euro based account..
However if you have a Nationwide FlexAccount (and a small number of other banks and building societies) you can use a debit card to withdraw money from ATMs throughout the EU without any fees and get money market rates. In September 2009 I was getting a better rate than quoted as the exchange rate on the BBC "markets" pages at the end of the day.
Many of the high street banks will charge a fee for drawing money out on a debit card.