Thanks for the input all.
Another strange thing...and I've have this happen to me before on my Sportwagon
I'll get in and try to start, it'll turn over slowly and eventually give up. I'll then make sure everything is 'off' ( lights / radio etc. ).
Re-try and it'l go click click click sound that could be the starter motor.
Now the interesting / weird bit. If I then try to jump start it, when I connect the cables ( with SW ignition 'Off' )
there will be a very big spark when I connect the cables and the engine will turn over once or twice.
The cables will get very hot - so the battery is obviously under load.
I disconnect the cable sharpish - and the only way I can proceed is to disconnect the SW battery terminals completely and then use a charger on the battery for a few hours ( thereby giving up on the jump start ).
This was the scenario with the GT this morning - tried to jump start, GT battery under heavy load, wires getting hot,
me abandoning the jump start and getting the RAC to visit - ( hopefully they can monitor the battery health / charge health etc. ).
WHAT CAUSES THIS INABILITY TO JUMO START THE CAR?