Hi bong-head
ALL I SAY BELOW IS NOT THE ADVICE OF A QUALIFIED SPARK. IF IN ANY DOUBT IGNORE ME AND GET A REAL ELECTRICIAN TO DO IT
I done it last week. B&Q is the place you need to go. You will need the dimmer with a little pic of a fan on it. DONT use a normal light dimmer. They only sell one of them and it'll be well hidden (was at my local shop anyway). You will also need a back box thingy because the dimmer does not come with one for some reason.
It was very easy to wire-up. You will need to strip the outer off the power cable of the fan lead and cut just the live wire.
Now connect the wire that comes from the Plug end to the bit on the dimmer marked C.
Now connect the wire that comes from the Fan end to the bit on the dimmer marked L1.
Try and use a wire stripper if you got one, makes it allot easier and neater.
Screw the dimmer on to the back plate and tape up the other cables to make neat and tidy.
Job Done :-)
Total cost £20 if you need to buy wire strippers.
Works a treat.
There are some more detailed threads on here that will give you pics/diagrams if the above was nonsense!
here is just oneSweet dreams
Bert...