They pre-authorise an amount on your card. Used to be £50, so you couldn't get away with with using a prepaid card loaded with a few quid. Maybe you can try to use at weekends so balance isn't taken until Monday. Might be able to get 2 or 3 times more than you put on the card.
dosn't work with prepaid cards, but they do work with bank cards as at the point you will only be charged 1 gbp, the rest is charge on the next day, on weekends you can milk a lot
My friend opened 2 or 3 UK bank accounts online one day, but the fact he already had a UK bank acc. it may have made it easier. I have yet to apply online for acc here in UK myself yet, once i do i will inform you of anything necessary.