Ford Escort Revving Uncontrollably

From Essex, 1 post

I have a 97 Ford Escort which has recently started revving uncontrollably during a journey.
Its fine when the car is first started, but once the engine has warmed up the revs go through the roof, i might as well have my foot welded to the floor.
Once I have pulled away I can take my foot off the accelerrator and just have to break and use the clutch to change gear, it doesn't need me to touch the accelerrator.
If I go on a motorway or dual carraigeway, when i leave that road the car is fine, but on the morning drive into work its a nightmare.
This has led to the car cutting out on a couple of occasions and it takes a few minutes to re-start, often for the revs to go up straight away.
does anyone have any clue as to what may be the problem?
Im getting it put in for a service next week, but it would be nice to have some clue as to whats been causing the problem in the first place.