Engine cranks but wont fire (1.5 Diesel)

[TenMillionFireflies]

OK, ill try to keep this short. My Saxo recently died and wouldn't start up unless using easy start. I went on a 120 mile drive and everything was fine on the way there, i parked up switched the car off for a maximum of 3 minutes. Came back to it and it struggled to start up, and when it did start it was belowing white/grey smoke from the exhaust (Ive had it confirmed by 2 mechanics that this is not the HG going but they are unsure what it is, allthough one did suggest it was RedEx burning instead of diesel)

So i decided to leave it and let her cool down, plus i didnt wanna be pulled over for having a very smokey motor! The next day the car failed to start at all no matter how hard i tried, so eventually i called breakdown who managed to get it going with some easy start.

Once it was going she wouldnt idle, she revved herself up a bit 4 times and then died. If i accelerated she revved fine apart from smoking so much the entire street was white!

In the end i had it towed back home where i loosened the injector unions and tried tow-starting it (recently changed the fuel filter so thought there could be an air lock in the pump). Even this wouldnt make her fire, and instead the engine was just turning (fast enough so the temp and oil light went out and the alternator was charging the battery).

Does anyone have any ideas what this could be? The one mechanic said a very severe air lock in the fuel pump, and another said the fuel pump has haid (although it still makes a click sound when first turning the key)

I did buy a fiesta for using whilst worked on the Saxo but the cam belt snapped on that yesterday and destroyed the engine.

If it's any help, i added RedEx to the fuel about 140 miles earlier due to its MOT approaching and the emissions getting a bit bad.