Thanks for all the replies. With those in mind I had another crack tonight.
Checked everything I'd messed with and couldn't see anything a miss.
I checked all the plugs for sparks again and they seemed fine.
I checked the injectors again and they still made splotches on a cloth, about 2" round after a few seconds, which seems okay I think.
I re-charged the battery last night and that was showing a 13.2v
Yes the fuel pump does prime. I tried priming it several times before ignition, to make sure the fuel rail was well charged.
No fuel leaks.
I checked the vents and hoses for blockages and they all seemed clear, I even blew though them to make sure - lovely
I tried swapping the 4 relays around in case one was duff, but didn't notice any changes.
I checked the compression again and still okay.
I checked in the tank and the new fuel filter was still all connected up and everything.
What really gets me is that it doesn't even think about firing. The instruments light up, the fuel pump primes, the starter turns briskly, but that's it.
Could it be that the fuel pump or regulator got damaged when she was leaking fuel and now she just isn't putting out enough?
Could it be the ECU just getting the sequencing so wrong that she can't fire any more? Need a remap or replacement?
Could it be the main relay next to the battery? It's the only odd one so not so easy to test.
All it can think now is to try replacing more stuff.