Vauxhall Corsa Car Wont Start. No Garage Has Answer

Hi, I have a 53' Corsa C 1.3cdti and it will not start. The engine turns over but it just wont fire. Garages have done a variety of replacements, this including a new fuel pump, new glow plugs, new injectors and also had a new clutch. I have tested the glow plugs and they are all receiving sufficient voltage. Can you advise on what the issue could be? COuld it be related to the TIming? Or maybe even an issue with the dual mass flywheel?

The situation has got worse, starting from a year ago, where it would start after it turning over for approximately 35-45 seconds, and sometimes even longer, now it wont start at all. When it would start, it was as if it was gaining momentum, like running on one cylinder, then 5-10 seconds later, running on 2 cylinders and so on till it got going. When managed to get started on a tow, it runs pathetic, there is no power whatsoever and very smokey. Had computer on it and brought up issue with EGR valve, but had that free'd. Wouldn't think that it would cause it to not start mind.

Any help would be gratefully appreciated.

Many Thanks

John