freelander td4 starts when it wants to help!

Hey

im hoping someone can help me with my Freelander, its a 2 litre diesel TD4 52 plate manual. basically what the title says, it can start one day pop to the shops, come back out and it just wont start, all lights come on, on dash, it keeps turning over but just wont fire up. Also the pump does not come on behind the driver seat, its silent. I had the same problem 6 weeks ago, which i was told was my battery in my thob and to replace the thob battery so i did and havent had a problem until last week, i had to leave it at the shops, next day i went back to it and started again fine. Any idea's to what this could be?

Thanks

either a faulty fuel pump, if you can't hear it running when you turn the ignition on,

or:

faulty injector (leak back test)

or:

camshaft sensor (replace and retry)