Thanks for the replies chaps!
Yes I thought something might have jammed inthe pulley belt too, but all appears ok.
I can rock the car back and forth and the rear wheel moves slightly as it takes up the backlash in the bevel box and drivetrain. Clutch works fine but as I let up the peddle the engine would eventually stall if I don't depress the clutch Again.
The reason I think the problem lies in the gearbox is that if I select a gear and don't push the gear lever fully home it will jump out when I rock the car back and forth. I think my next move is to take off the gearbox covering and check the gear selector mechanism as I think it might be stuck in two gears. I will keep you posted. Cheers! johnml