I'm assuming I've got to bet £5 of my winnings a total of four more times until I'm allowed to withdraw it. Is that correct?
Use oddsmonkey (http://www.oddsmonkey.com/) to find an event on which lay odds are very close to back odds (using your preferred betting exchange). Bet on something that you that provides a good percentage yield that you think is unlikely to happen (at 888bet) and lay this bet on Betfair (or other exchange). If it doesn't come off, you 'win' at Betfair and extract most of your winnings without having to rollover multiple times. You can do this multiple times until you can either withdraw from Betfair, or you've met your rollover requirements. Will require pumping a bit of cash into your Betfair, but overall you're unlikely to lose much of your winnings as long as you pick something sufficiently unlikely to occur to lay on Betfair.
Does this make sense? Use this (http://www.matchedodds.co.uk/matched-betting-calculator/) to calculate the amounts required to lay on Betfair/expected returns without risking arithmetical miscalculation (and potentially losing winnings).
Let me know if there's any of this that doesn't make sense - if you follow these instructions, you should be able to get your winnings out (via an exchange) without having to meet the rollover requirements.
Cheers, mate.
I managed to double my money so all is good.