They usually cut 2 of 3 circuits (for thatcham certification), fuel pump, starter and ignition are the 3. I’d say as the fuel pump is being heard to prime and it’s cranking the immobiliser is a red herring. Knowing the crapping wiring on these (my vrs was a nightmare) I’d be looking at the connectors and for a broken wire going into the ignition or injection circuits.
Plug out first and lay it on the block and make sure you have a spark if you do then pull an injector and put it in a jar if you can and crank and make sure it sprays.
Probably check both crank and cam position sensors (if it has cam sensors) and wiring to them, a crank sensor will stop it dead but a cam sensor will usually result in a start and ability to Rev but it will die when you let it idle.
