No-one ever really checks out here in East Anglia, if you do get caught, I think it was like £10, maybe £20. Also a good thing to do, at stations you get permit to travel machines. You get these if you don't have time for tickets or something, then you pay at the station you get off at. Get one of those for like 50p, then if you get caught, say you nearly missed the train and pay then. In the likely case that you don't, you get it for 50p.