If I wanted to transfer 2 or 3 balances onto one credit card (total would be just under £5,000) does anyone have any advice on which credit card would be the best to use? Not sure whether to go for a 0% for 15 months or a low monthly interest one. Also have to take into consideration the admin fee for the transfer which can very from 2.5% to 3%. I'm sick of paying such high interest rates but can't afford to pay off all at once
That's what we tend to do, swap about as we are offered either 0% or the lowest interest rate on offer. Yes you have to pay a premium for doing it, but in the long run it's cheaper than paying 19% or whatever on the cards when the 0% runs out.
Why don't you also consider getting a credit card that won't charge you interest on any new purchases for a set amount of time, you can then take the money you would have spent on things and put it towards paying off your old bills - or put it in a high interest savings account.
http://www.moneysavingexpert.com/credit-cards/best-0-credit-cards