Nope. There is a wee box you should tick when you signup (or you may have to go into the promotion area and opt out) that stops you from playing with bonus money. It's just a big con.

Withdraw the £10 you have bet, as you have 'staked' this, so you've qualified for the cashback. The £20 bonus is free to play with, but you'll need to 'flip' it 500% or something.