Volkswagen Golf intermittent over revving

Hi

My X Reg VW Golf has an intermittent problem in that it will start fine, drive normally for quite some distance and then start revving to 4500 revs, On stopping at traffic lights etc the car dies, to the point of cutting out all together when pulling away again. The problem seems to cure itself for sometimes months at a time but then returns, there doesn't seem to be any pattern to it in terms of cold start etc

Any advice gratefully received