Gearbox isn't dead!

Anyway, once in the garage and advice sought from http://www.landyzone.co.uk/ it turned out to be the handbrake of all things! The handbrake works on the transmission rather than brakes (basically uses a drum on the prop) and although fully off in the cabin, the connecting rod wasn't fully disengaging the handbrake. Once it was all cleaned up and greased then no problem anymore :)