Start simple. Go to Maplins and get a multimeter for £5ish.

Measure battery, report back with voltage.

12.7v is good.
12.4v is 50% flat.
Anything close to 12v and you’ve probably found your problem.

Then get it started and make sure the voltage is in the range of 14.4v to check its charging.

If its only struggling with hot starting, it could be the camshaft sensor.

You really have got to get the car to a tech who knows how to read his diagnosis readers,
big failure with damp bsi ( car wash) are symptoms I said above, but they can just die with other failure modes.
My best guess and it is a guess with intermittent starting is an internally broken fuel pump relay wire from relay across engine to ecu. Load testing the loom is the only way as this fault can pass enough low current to illuminate an LED tester.
Big clue if it is this is lack of comms when in fault state, and the yellow eml light won’t be lit on the dash with ignition on, all others will be lit as normal.

Again I emphasise that’s all a guess.

Another guess is someone keeps swapping your engine for a piece of Swiss cheese…

Spooky – battery is brand new and I have today topped it up and checked the voltage.

Ulysse – well it’s no longer intermittent starting! It refuses point blank now. As far as I can tell all lights on the dash are as normal. I shall indeed have to get someone to look at it somehow :-/

Has the hallmarks of a cranksensor

You can buy a cheap odb reader for a tenner.

If it does live data you can see the rpm signal

Eurocarparts / FPS/ Andrew Page love people like you 😉
It’s the crank sensor…
Nope, Doesn’t work :/
It’s the cam sensor.
Doesn’t work:/
It’s the fuel pressure regulator….

Test and prove your theory, bearing in mind if you don’t understand how something works, how do you hope to test it?

I reckon you’ve got some corrosion related electrical problem.
I would check & clean up all the earths,likewise all relays & fuses/fuse holders.
HTH

id plug in diagnostics….

you realise how many contacts youll have to clean up in any modern car bustaspoke ? its not a rover a series 😀

Hell wire the radio up in a modern car and theres a good chance it wont start.

Hell wire the radio up in a modern car and theres a good chance it wont start.

I’ve bought loads of cheap M59 berlingos with that fault…

You can buy a shitload of sensors for the price of a dealer plug in

Sometimes it’s much cheaper to try the obvious options before paying someone else