Problem was caused by air getting in (Only When Cold). After cahnging lots of bit I found by accident that if you remove the ait filter unit and bits of plastic that on the top/rear of the fuel filter housing is what appears to be some sort of valve. This was bleading when cold and letting in a small amount of air. This cleared once the engine block heated up.
I bypassed the fuel filter buy puting a simple in-line fliter and thje car is fine. It has nevewr run better.
BobH
November 2006