NIL
Backing out of my original BACK BET by placing a LAY BET at lower required odds and appropriate Stake puts me into a “No Lose” situation.
If Pella WINS, as I hoped he would, I will have to payout £170.00 to the person who has placed a bet with me, but on the otherhand I will make a profit of £190.00 from my BACK BET—a net result of £20.00 Profit.
If Pella LOSES, I keep the £20.00 Stake Money which someone has bet with me. This £20.00, less the £20.00 I staked on Pella to WIN, gives me a net profit of NIL.