Welcome to the club, Mark.
I also think its is a fuel problem. I am assuming your car is a diesel, and if so do you use Premium fuel? I find it gives better fuel consumption, as well as being a cleaner fuel.
I would be inclined to pit in an additive, Diesel Magic costs under a tenner and will give the fuel system a good clean out.
Let us know how you get on.
Regards,
Peter.