Thanks all who have replied - here are the answers to some of your questions!!
They didn't change anything at the service and they said that they didn't tinker with anything either!
I have had a play with the distributor and the power cable was definitely loose but it still doesn't feel right now! It doesn't seem to have all that much power and seems noisier than normal!
:?
I came across another problem at the weekend - i was changing the rear brakes (discs and pads) but couldn't loosen the bolts (alan key head) that hold on the carrier? any ideas of how best to loosen these as there isn't much room to play with! Also they seem to need a 7.5mm key - isn't this a bit of an unusual size?? Finally does anyone know where i can find replacement bolts in case i have to destroy them to get them off!
Cheers all