Yes they are widely used, harder for you to get one here and you have to have proven income etc, and the interest rates willl bleed you dry. Probably better using uk CC if they give you good exchange rate, but I dont know what rates the UK banks give on CC transactions

They give you the tourist rate at the time of the transaction plus a surcharge on top for doing the transaction which is different from bank to bank, you will need to look at you particular banks terms and conditions to see what the rate is. The only bank that does free transaction is Nationwide provided you have an account with them.