Gearbox / Clutch issues?

I was driving home this afternoon and the gearbox change went very stiff. It needs an arm like Popeye now to change gears. The strange thing (to me anyway) is that the gearbox works fine when the engine is off but becomes stiff when the engine is on. I've got the local garage to have a look at it tomorrow for me but I'm fearing the worst! Anyone had any experience of this at all?

Thanks in advance for any replies.

(55 plate A3 2.0T Quattro)