Couple of offers that might be useful to the gamblers...
Place a £10 bet with Betfair and get £26 cash-back via Quidco
http://www.quidco.com/betfair-sportsbook/?hoid=29157
Place a £10 bet with William Hill and get £27.30 cash-back via TopCashback
http://www.topcashback.co.uk/william_hill_sports_betting/
Offers are for new account sign ups I think. The cash-back sites are both fine but the money might take a while to come back to you, usually 2 weeks - 3 months as a rough guide. These two companies probably have some 'free bet' offers for new members so might be a bit more of a deal to add on?
Total £20 stake would give a £33.30 profit even if the bets fail.