Crikey theres some accountants on here!
£50k = £250 a week for 2 years = enough to have 2 years of absolutely epic fun.
Rent out your house on one of those gaurented income thingies to keep the mortgage paid, and f*** off to somewhere fun!
I'd buy a big sailing boat (OK, not that big with 'only' £50k, but big enough), a custom Nicolai, and go on the most epic round the world trip ever with as many mates as could afford to keep up! Simples, just tow macral lines 24hrs a day and you'll be eating fish till your sick of the stuff, add a solar still and your sorted for life!
Just need to draw up a list of places with good riding within spitting distance of the sea :-p, I'm sure the caribean and Hawai must have some epic trails.