I would do some research into pre-paid credit cards as they are known. There are numerous companies offering these including the Post Office, Thomas Cook, etc. Some are better than others as they have different fees and terms attached to them. Some of them you have to pay if you don't use after a certain period.
Ones I have seen recommended are Fairfx, Caxton and NetTeller, but you need to read the T&C's carefully.
Have a look
HERE, but I would suggest searching on that site as there is probably a better topic which explains how they works and the fees involved.
luci