Drive Train swap

One other trick you can try to narrow down likely problem sources is to carefully connect a jump lead to the terminal on the starter and with the while someone turns the ignition key touch the other end of the jump lead into the battery. If it turns over then you can rule out starter and battery and look at cabling or immobilizer

Edit: yes as my learned colleague points out, you do need a long jump lead for that but if you are careful you can clip two together - just be really sure to keep the clips in the middle well clear of the bodywork!

I had this happen to me bad earth, worth a check

If it was an issue with the immobiliser it would either not turn at all or would turn but not fire.
The system isn't clever enough to know that it is low on clutch, brake or even coolant fluid or oil.
If it was a low battery I would expect it to click a lot and the coolant fans to start.

I would start by taking the plugs out and turning it over by hand.

Great Thx , Lots to work on. I can see my next weekend being busy . I will feedback once I have tried these suggestions C