Hi Laggy,
it sounds like the float valve is stuck in the open position, this will allow fuel to be pumped through the carb even when the engine doesn't need it. The float valve is a brass needle valve which is screwed into the carb float chamber top plate.
It may have got some dirt in and stuck so will probably just need a clean out, but I think most carb rebuild kits come with new ones if needed.
I've always found it useful to fit an in-line filter (one of those cheap plastic ones with a paper cone filter inside) between the fuel tank and the pump. Most old VW's seem to have some dirt and rust in the tanks.
Cheers.