Well I don't know how new the car is but this is often terminal in a financial sense. if you catch it before it goes through the engine it's not a disaster but otherwise the engine is at best in need of stripping down and at worst kaput.
all they will do is drain the tank and fuel lines change the filter add diesel and a fuel additve should only take 2 hours to do at the most and should cost no more than �200 at the most
possible fuel pump needs replaced as diesel is a heavy oil it lubrictes the pump, if it has been starved of lubrication the rotor in the pump could be worn.
Thanks for all your help everyone.
We took it to my boyfriends garage and one of the mechanics drained and managed to get it going and now its running fine, it only cost �200.