There are a number of pre paid /debit/ATM cards around , you will want one which carries the Visa or MasterCard logo, try www.mygcard.com or www.globelxchange.net they both work well.

I don't know if it exists in the UK but I have a Visa Check card which is accepted everywhere, for me it is better than an Amex.

Good luck and let me know if you have any problem with them.

Regards

Chuck