1.7CDTI Starts with a clatter, dies, STARTS ITSELF?!

[TechBeard]

Howdy!
I am hoping someone will know what on earth is going on with my faithful 2013 Astra J 1.7CDTI SRI EcoFlex. 
It's starting to do something very weird after you try to restart the engine when it's hot. So for example in the video below id driven for 40 mins, stopped at a restaurant for about 30 mins and then tried to restart the car. 
If you leave your foot on the clutch the engine tries to start with a horrible clatter, then dies, then STARTS ITSELF! then dies, and repeats this process until eventually it starts. I have found flooring the throttle does seem to help make it start faster. 
There are no codes on my OBD2 scanner, and it does not happen every time, but is certainly worrying when it does.

Does anyone have any idea?

Youtube issue of issue

[TechBeard]

Someone suggested giving it a diesel flush treatment which I didn't have time to do, so I did a double shot of Millers Diesel treatment ahead of my monthly trip from Cornwall and Essex and back and since then I must say it has not happened again (and the car sure does drive better with no knocking or anything and lots more power) so perhaps was just a clogged injector?

I did order a new Crankshaft sensor but I think ive got the wrong one as the spacing between the sensor and the bold looks different, and also despite best efforts I could not reach the dam thing anyway.