Hello, I have/had exactly the same problem. Forgive me for my lack of technical terms but i'm not really that competent with car mechanics! But anyway, originally my mechanic thought it was a leak from the switch (maybe a solenoid) on the fuel line just where the fuel-cut off for the immobiliser is located. The switch was very hard to get at, taking him all day to remove the reinforced protective cowel. It was changed and it was thought the leak was fixed, however it turns out that it was still apparent. Currently, the injector pump has just came back from getting an overhall/rework and the leak is fixed, allegedly, but i can only tell whenever i get more than 250miles out of a tank! So, maybe the problem lies with that switch, or if this is a common fault, then it's more than likely something leaking/a loose connection with the pump!