So found the best for me using moneysaving martin
Its 0% on purchases for 12 months. I can do a balance transfer which will cost me 2.5% and then be charged at 2.9%.
So my question is how do I know how much to transfer. This month I am paying £150 off the balance, so do I transfer whats left after that, plus anything Ive spent? Do i then stop my dd to old card?