Well, good news and bad!
Good news is that after a lot of faffing the sump is finally off.
Bad news, I only found one more piece of the cam in there. This means that so far I've found about a third of what broke off.
So not sure what to do now. Do I stick the sump back on and crack on driving it in the mad hope that the other bits will work their way out then check the sump again in a few weeks? Or do I have to go through further stripping to try and find the bits?

You can buy a small camera that plugs into your phone. At least you can if you have an android. I'm not sure if apple support such devices though.
With these cameras, you can check places you can't see from below or above.  Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Good point. I think I've still got one of those somewhere. I'll give it a go but if I don't find anything not sure what to do!

Before I get myself into another arse of a job is it worth checking the oil filter? Is it in the realms of the possible that some bits could end up there? Not sure how big the oil passageways are to the filter?

It unlikely that anything other than tiny particulates got through to the filter, as bits would have to pass through the pump, destroying it in process. The pickup screen might have caught some larger bits, but this is unlikely if the engine stopped shortly after the drive slot failed.
The bits will be stuck inside a ledge in the block or maybe on the balancer shaft assembly, unless the cam drive slot was damaged before the cam was even fitted. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

I understand that if they're on the balancer shaft it could end up being catastrophic. Just looked in Haines at removal and they say it has to be done by a proper mechanic/specialist although in that tech manual it does give a bit of an explanation but there are special tools required.
I've tried the endoscope I've got but it'd crap! The picture isn't great and every time I move it, it disconnects!!!! 😡
Ive tried getting into every area I can with a magnet and a flexible drain cleaner to see if I can dislodge anything and I've hand rotated the engine. Nothing.
At a bit of a loss now tbf. Was so hoping if find five pieces of broken camshaft in the sump!!!! !

This is a bit of a long shot and I'm probably clutching at straws.
I've just been looking again at the broken cam and matched the couple of bits I've found so far to where they broke off. I've attached a couple of pics. What is unusual to me is that there are worn, flat, shiny bits on one side of each broken piece. As though the fuel pump key has been forcing against it. Might just be me but it looks unusual. The other surfaces are rough and jagged but these are as though machined flat.
Could the pump have still operated with just those bits attached to the cam?
I'm wondering whether I'm chasing bits that have already been recovered during a previous issue?

Got everything back together. Primed the fuel system. Now getting fuel to the rail. Still won't start!!!
Getting P0088 Fuel Rail Pressure Too High and P02E1 Diesel Air Intake Performance!

Omg. Don't believe it. Changed the fuel pressure sensor, basically put the old one back on. Started up straight away!!! Just goes to show what people face said about new parts.
I'll not get too giddy too soon though!!!!!

Glad it's working again.
I suspect that the cam has been broken for a long time, and the pump drive has just been hanging on until it couldn't any more.

It's possible that the replacement pressure sensor needs calibration, like most other sensors on these engines. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Well, lasted one short journey to the park to walk the dogs.
Firstly, when I test drove it around the work car park I noticed a splash trail on the floor where I'd driven. Checked under the bonnet and it was wet! Injector 1 on the right as you look at the engine was peeing fuel up through the sides! Took it out, cleaned it and the bore again, refitted it and all seemed well.
Drove to the park and it developed a bit of a chug and I noticed what looked like vapour coming from under the bonnet, just the odd whisp. Had a look and it seemed to be some of the residual fuel spill burning off/evaporating. Driving back it went into Reduced Performance again and conked out. Checked with my new code reader and it was showing 2 crankshaft sensor issues. I'd changed it when I was searching for the culprit of the original problem. Luckily I had the old one in the car. Managed to swap them at the roadside and it stated up no problems.
It drove fine but the chugging got worse and everytime I stopped at lights exhaust smoke was coming from under the bonnet very clearly. I got back the short distance and looked. It seemed to be injector 4 this time pumping exhaust gases out.
Stupidly, I'd cleaned the infectors and bores up as best I could but I hadn't taken the copper washers out and changed them. I was lead to believe it needed yet another special tool. However, I had a threaded rod about form a previous job. I ground the lead end down a little to give it a bit of a shamfer and I managed to lift them out. So getting new ones next week and will put them back together. Stupid of me not to do it in the first place but I thought the clean I gave them looked good enough. But clearly they get crushed so taking the crud out probably opened up gaps?
Are the rubber collars on them with the slight ribs in them to seal them also? Or are they just to keep them stable in the bore?

Glad it's finally working correctly. Oh and no you can't reuse the old copper washers. I've had aftermarket copper washers fail to seal (too hard) too, so only use genuine PSA washers now. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Hi
Just been up to my local Land Rover parts place this morning and bought the appropriate washers for my model and year. Also ordered new rubber retaining sleeves that go on the neck of the injector. My cleaning/cutting tool arrives sometime today so hopefully have them back in by tomorrow evening!!! 🤞

Amazing thread PK… I’ve been following as I too have P0087 error - Fuel Rail System pressure too low…

Saw some diesel around injector 1 - fixed that yesterday but hasn’t fixed my cutting out issue of fuel rail pressure codes. How are you getting on?

Hi
Mine is going ok now. Been up and down the motorway in it and to Wales for a couple of days and it's fine.
The only thing that it now has is a noise when accelerating quite hard. Difficult to explain the noise. It starts to sound like an old VW Beetle if that makes any sense? A bit like the noise made when kids put cards in their bike spikes, but not as sharp a noise. Not sure what it is.
What's the problem with yours? Is it running at all or does it not start?