Rates change frequently, so there can be no definitive answer to your question.
However, irrespective of whether you're changing pounds to euros or euros to pounds, Marks & Spencer and the Post Office usually have better rates than any of the firms that trade through travel agents.
The best rate of all, though, can often be found in your workplace or within your family. Simply find someone who's travelling to Euro zone in the near future and offer them �390 for a little less than they'd pay at the Post Office. Then you'll both be in profit.
Chris