i did a search and found loads of threads on this and it seems it could be anything.
I checked the hoses last week and they seemed fine apart from a light misting of oil inside them

Click image to enlarge

Without more information about the driving circumstances when you get the problem it is hard to be specific but check:
1. Top LH (as you look under the bonnet) intercooler hose for splits
2. Condition of MAPT sensor for that side. It is mounted with a single screw in the top of the inlet manifold just behind where the intercooler top hose joins the manifold. If it is gunged up with oil clean it off with brake cleaner. If necessary replace the sensor.
3. Electrical connector to the MAPT sensor
4. Sticking turbo vane linkage on that side. Can be lubricated with 3 in 1 spray oil from underneath and through wheel arch. You can observe it operating when you switch on the ignition
5. Split in the plastic inlet manifold itself.
Let us know what you find.. Previously a 2008MY Tonga Green Vogue SE 3.6 TDV8

Thanks. The hoses are both ok.
It did it twice last night on the way home. I was driving along a flat road and was just driving slowly when it happened. I stopped and restarted it and it cleared, but then faulted again. Restarted a third time and it was ok after that.

I have noticed a strange noise when I turn the engine off. It’s coming from under the drivers side front wheel arch and sounds like a car being jacked up with a squeaky jack.

That sounds to me most likely to be the variable vane turbo linkage I mentioned. When you first turn on the ignition and when you turn it off it goes through a few cycles of actuation. There is a link rod and a couple of pivot points connecting the actuator motor to the variable vane actuator on the turbo. Those pivots suffer from exposure to atmospheric muck and can seize up over time, sometimes stopping the linkage moving smoothly or sticking at various points. If you search on here for turbo linkage you should find more information and photos about procedures to inspect and lubricate the linkage.
Basically the fault code is generated when the MAPT sensor doesn't see the boost pressure from the turbo that the ECM says it should see. That can happen if the linkage is stuck or sticks. Previously a 2008MY Tonga Green Vogue SE 3.6 TDV8

just been out to see if I could see the linkage and it’s just visible. When I turn the car off I can see it moving from one way to the other but it’s slow and almost snaps across like it’s sticking.
I’ve just blasted it quickly with WD40 as I’m limited on time on the way to work etc so I’ll see what that does.

Thanks for the pointers

Still faulting.

How do I check the inlet manifold for cracks? The flutter noise I can hear sounds like air escaping

i believe a smoke test will reveal cracks..