The only problem I had was with Sportingbet, they are absolute scum, if you do match betting, avoid them! They advertise a £50 risk free bet, I bet £50 and lost, they refused to give me the £50 free bet without any reason at all and said they can do so because it's in their T&Cs (doesn't sound very legal, do I have a leg to stand on if I report them to my bank?)
Did you lay your £50 bet at an exchange? If you did (and you chose wisely with the odds) then you won't be more than a few pounds out.