Hi there
When were the spark plugs and leads last changed (full service).  This happened in our escort and turned out the spark plugs had worn, so I changed them (and the leads for good measure) and it solved the problem. Changing them is really simple - if you have a haynes manual it will explain it in there.  If not, nip to Halfords and read up on it there.  It's not a mega job -it only took me 10 minutes.
HTH
                
 Caroline Jones
                
 August 2008