No offence at all! Sometimes the obvious questions are the best ones! I have double checked the fuel filter connections and it looks ok as far as I can tell. I assumed if you connected the pipes incorrectly, the car wouldn't start at all, or would it??

Dodgy fuel filter is another possibility but I did buy it new from halfords. Can they often be deffective from new? I will have to get a garage to check this for me as I don't have a pump/primer to install my own fuel filter.

An update to the power issue: I took the car in to a garage the other day and they said they couldn't see what was wrong despite sending three of their staff out for a test drive!

Stranger still, I took the car out last night and this morning and it seems to have gained back some of it's power. I don't think it's quite back to how it was before the filter change but it's defninitely better. I'm still just as confused about this! What could the problem be if it's able to fix itself over time??