Thanks everybody for your comments yesterday.
I have checked and it was running on 3 cylinders.
It is getting a spark and fuel but the plug looks brand new.
I am now guessing that when the valve in that cylinder has been damaged when the cam belt slipped. Unfortunately my compression tester has the wrong size thread for the zetec.
Looks like the head is coming off...



Cheers

Frank

Bugger

Usually get lots of valves bent in different cyls with a slipped belt. Are you sure its not a sticky lifter?