From what you've said I'd suggest that, if it does turn out to be a security based issue, the Autowatch immobiliser is the more likely source of this problem, simply because the Subaru transponder based immobiliser will allow the engine to turn over on the starter - it just won't allow it to start.
If it won't even turn over, the other obvious causes would be a duff starter or key switch - although one would presume that the very nice man will have ruled these out.
If it is security-related, the inference is that the non-factory fit immobiliser locks out the starter circuit, and that the immobilisation relay is past it.
Thanks for the replies, the Autowatch does have overide process in case you lose the key, but when I made a brief call to the guys that installed it he said the overide process (Another company posted the proccess here http://www.abacuscaralarms.co.uk/man..._prog_keys.pdf ) doing the overide would only disable the unit in the same was as the key.
Car wise no unusual locations just in the road at the girlfriends.
What did seem odd about the factory immobiliser was even without the key in the igntion, I can't recall seeing the key symbol on the dash flashing it's LED to indicate it was armed.
Have had the car in the dealers and have had a partial resolution. They said it seems the Autowatch Immobiliser was faulty which stopped the car even attempting to start. Immobilised through the crank signal line according to the garage. Started after they replaced the Autowatch unit.
They did find though the OE immmobiliser lamp still didn't work.
Picked the car up Friday and all seemed initially ok, went to back to my family last night no prob.
Have had to return the Scoob to the dealers as of lunch time Saturday. Went out 9am started car for 30 secs no problem then went back in the house.
Went to start it at 10:30am and it would turn over quickly but not start, or vaguely kick into life then die within a couple of seconds. Kept doing this very occaisionally starting. Anyway as the garage was 30 odd miles away I got it running and back to them to investigate further.
Any ideas? As it seems to start then die wondering if something up with the factory immobiliser too?