There is a very good article on this site about changing money,
'Don't use your bank to change your cash to Euro's
As a rule of thumb: how much is your your money going to give you oneyou do the transaction to Euro's, minus the charges? and don't forget to ask the exchange broker/bank to charge you in England any fee's to be incurred by the accepting bank in Spain, HSBC charge about £10.00 per transaction. If your Spanish Bank try and charge you again in Spain because you have a non residents account, that actually contravines the European Banking Laws , So Ask For Your Money Back... that is the law.
Hope this helps.