Yes, exactly. As h9826790 suggested, the power cable is nothing special, and I suspect he was NOT referring to a plug adapter - although that would work fine, as well.
Anyway, it's a standard power cable - easy to find when you get to UK.
You would get one just like this - http://internationalconfig.com/icc6.asp?item=83221
I think you would be getting a spare for the original power cable, so that would be a service replacement part. You would probably have to ask at a UK Apple store for that - if you want the exact part that Apple supplies (and pay the Apple premium on that, too! )
Why not just get a mains cable? I think in UK that is usually called a "kettle lead" http://www.cablewarehouse.co.uk/dis...MIr6PWl8nF3wIV0lmGCh2bqQi3EAAYASAAEgJe-vD_BwE
There's even white cables, find those by scrolling down!
You would be spending much less, for the same quality as the Apple part. Good stuff for less than £2.-