Alas, one for 2024

I have been in the habit, laid up mid 2018, of starting the car, letting it idle and come up to temperature and having a little drive around the yard; probably twice a year.
In 2020 I had to replace the expensive fuel pump relay as the car would not start and there was no fuel pump sound from the offside. Since then, starts on the button, runs well. That’s the only snafu I’ve ever had in 15 years of ownership.
The other week, transport arranged for a swap with another car to my hobbies workshop to join a few cars up there and hopefully a season of running around in the Scala.
Get to the point!
Ah, yes, car turns, fires in no time at all, runs for 1 or 2 seconds then stops, leaving the fuel pump whirring for a moment.
Turn the key, fires up, stops again.
I’ve swapped out the fuel filter, enormous pressure of fuel the engine side of that, no luck.
I’ve sucked out 12l of fuel (from filler as I couldn’t prise the lift pump cover and it’s only turn a fraction with an ‘ammer and driver/blunt chisel).
That left 1/3 of a tank which was topped off with 12l of ESSO Supreme (which all my older motors enjoy as 0% ethanol).
Still the same, starts on the button, dies after 1/2s.
Unplugged the blue connector ?5th injector. Wouldn’t start at all.
At a bit of a stump now. I’ve read the pinned thread on the k-jet, cannot claim to be any the wiser, and will look at the warm up regulator filter next (couldn’t find one on the fuel distribution unit).
The fuel distribution unit doesn’t have any real pressure of fuel when I loosen the top fittings after the engine has ‘stalled’. Lots at the filter.
Tried running with the relay under the fuel pump turned sideways so the pump was running continuously; again nothing.
Took the air pipe and the car runs fine on easy start
Anyone any pointers for this dingbat in Wiltshire?
Thank you in advance
Griff