Went through all the connections today and nothing is wrong there.
All components seem to be getting the correct results when testing.

So now I have a theory;

Whilst I had the Crankshaft position sensor out I looked in through the hole
I rotated the engine until i could see the gap on the flywheel that is picked up by the sensor.
With the gap inline with where the sensor would be I went and checked the position of the pistons.
All pistons were close to being in line with each other. i.e. NOT at TDC
So - Should the gap in the flywheel correspond with TDC?

I'm thinking that when the "mechanic" put the flywheel on to the engine he hadn't put the dowel back in and so bolted it on its 6 bolts in the wrong position.

I'm doubting this "mechanic's" ability more and more as I find more bodges on the car