Thanks for taking the time out to reply.

I'm not sure about the coil packs, never had a car which has had coil pack trouble before, so maybe a good place to start looking!

** Does anybody know where the tank breather is situated? - wondered if that might have got blocked / trapped and not allowing the tank to vent properly causing a vacuum? I assume it must have one? **

The only other info I have is that it is the first long run it's had in a while and when I filled up at TESCO the tanks were being filled up at the same time and I just wondered if there was an outside chance this might have kicked up some sludge in their tanks which in turn I might have picked up blocking; restricting flow to the fuel filter. I would have thought that most unlikey though as I would have thought that once the filter is blocked it stays blocked until changed.