Could be getting air in the fuel lines somewhere, did you change the filter before or after the problem occured?

Right, that's the first thing I would have gone for. You need to check the fuel line from where it comes into the engine compartment to the pump. A good way of proving if that's the problem is to fit a section of clear pipe in the system just before the pump and watch for air bubbles especially whan you rev it. If its a Bosch system, leakage from the injector leak off pipes can allow air in, so just do a visual check and if they are leaking you can get a section of pipean an end cap for not to much money, I think Halfords do them.