Excessive Over-Revving Engine

[Sweekune]

Hello

I own an R reg Fiesta (1.25 Ghia) and recently whilst driving, my engine over-revs to 3000rpm when stopping or slowing down, usually when I dip the clutch to shift into a lower gear. The revs just climb until I come to a complete stop or change gear and return back to what is normal. The car drives and seems fine but the engine doesn't sound particularly smooth. I've read certain things around on different forums, etc and it seems to be a common problem but I am no where near deciphering what it could be or how to cure this problem. Any help would be highly appreciated. Many thanks.