Well here comes the answer !
I don't believe in co incidence as they are very rare indeed. However as mentioned the car wasn't that dead even 'with' the immobiliser so I was 'perplexed'. I called the spark who said it couldn't be anything he'd done ( suprise), I only re joined two connections which had been cut in to. mmm If I call him out he's just going to tell me its something else and charge me another 50 quid.
As I have Homestart so I called the RAC. I was hoping its the man who lives in my village because he's a good egg and he'll go the extra mile for a fellow villager anyway and at least try. He is impressed that I've tried jump start , fuses, meter on the battery to earth etc but I'm the first to admit that I don't really know much abouta cars wiring past the obvious.
I told him straight that a sparky had removed an immobiliser and after basic checks , I showed him that the sparky was fiddling around under the passenger footwell and had mentioned restoring a connection in there.
The RAC man after several other things , lifts up my fuse board and then says ' try now ' vrooom away we go. One of the large plastic connectors that plugs on to the bottom of the fuse board had come off as the clip had snapped off one side of it. This just happens to be the one that had a bypass wire cut in to it. The only way the RAC man could secure it was with a very long cable tie right round the fuse board but its now in tight awaiting a new connector when I fancy the job
In a way I don't blame the Spark because it might be that he removed it did the wire plugged it back in and didnt know the little plastic lug had snapped off , however the spark was too quick to insist ' it couldn't be anything I've done' and he could have been a bit up front and offered to come round and check without charging me ?. I think in that situation I would have done to keep a customer.
Back to finding the source of the fumes now which I am now sure are exhaust but boot and lights sealing hasnt cured it [

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Mas