This is not my car but my brothers, its the Mk2 shape but with the older 1.9TDI engine in. He is saying that every now and again the rev's go up to about 1500 and he has to kick the gas pedal to try and get it back to tick over of just below 1,000 ....... does not sound like a big issue but its annoying him. He is a tad vague with when this is happening but i think it can be at random times and not just when he first starts off, so he could have driven it with the engine warm... he starts it again a bit later and it happens then. Any ideas ?

Throttle pedal fault, it might respond to cleaning and lubricating, otherwise it needs replacing.

The 1.9tdi in our vw transporter does the same, not quite up to 1500 though. Maybe 1200/1300.

Itll just randomly do it. I dno why, but its always done it

It's as fordfan says. It may be a faulty fly by wire throttle pedal unit. Once they go that's it. However, before changing it, try resetting the throttle operating parameters. This is needed sometimes after the battery has been disconnected for whatever reason.