very bad shakeing problem

bit or a weird one for you if any one can help ive got a e reg 90 and use it on road and alot off road as have some really good green lanes local

now i drove to work fine yesterday reachin 60mph since then ive been back down a bad green lane and now any time i reach 40mph it sakes very very bad the whole car vibrates and the wheel turn a quater left then a quater right and back and forth with me holding on very tight what have i done ?

Check your wheel bearings and propshaft UJs. Have you knocked a weight off one of the wheels and it's now out of balance? I once had a really terrifying one and i turned out that my panhard rod was loose ...won't use that garage again!
Harry

thanks for the help sorted now it was the wheels had so much mud on the inside ive now spent a hour cleaning the mud off and now there fine thanks