Golf Mk3 immobiliser stops engine, will not start?

Golf Mk3 1996 TDi. The engine cut out a few times when driving and occasionally would start back up if I was lucky. Since then it is worse and simply will not start. It seems like an immobiliser issue. As far as I am aware there is no after market parts on the system.

I have bought new batteries for both remotes and no joy.

I have also bought a 109 relay and replaced it. No Joy.

I have also unplugged the immobiliser unit (located behind the glove box) no Joy.

I can fool the immobiliser if I plug and unplug the immobiliser box while turning the ignition and the car will start normally but I cannot go on like that.

Generally, The engine will turn but not fire. If I hot wire the fuel pump I can get the car to fire and run but the alarm is running constantly and the hazzard lights flash. How do I bypass the immobiliser so that my fuel pump will work but not set the alarm off. Or is it not an Immobiliser issue is it something to do with the antenna receiver for the immobiliser. but if it was this why would it cut out mid journey.