I had an issue with a D4 where we though it was the parking brake switch and indeed replaced it, and a couple of months later the same issue occured of the electronic parking brake not releasing. Fortunately I had Vagcom with me and was able to tell the handbrake to release itself!
On further investigation it turned out to be loose wiring / connections where the wiring harness went into the brake module in the LH side behind the boot trim. This was sorted out and all has been fine since - worth a check in case you are getting intermittent connections causing issues +++

Many thanks will try both. The BECM is in the post so we will see.

Update:

Brand new earth cable with the BECM arrived today and fitted. It was a brand new cable (no kinks) but the female socket for the BECM was smashed off leaving the two pins exposed which is the same as the one I took off. I have a third one on it's way on a slow boat from Lithuania which I ordered first.....
Anyway, no joy, still can't connect to the BECM. Looking at various various diagrams it appears just to be diode?

I tried leaving the handbrake off and the car still cycles itself back on (like the list above just without the Parking brake symbol this time. The P on the gearbox lights and the pump under the bonnet runs- rinse repeat.

I checked the cables that I could find in the boot all seem tight.

Scanned, all codes gone except the BECM no contact.

So Questions:
Does anyone understand the logic of which components can "wake" the car up? At this stage it doesn't appear to be the handbrake.

This is the only code that might meant something from the first scan but it has not re-appeared
02067 - Optical data bus unauthorized awakening request Intermittent
But I can't find anything constructive on the net about it and it's currently not a live code. Car still runs perfectly, just doesn't go to sleep.

Update:
took car to well regarded local diagnostics place. Hmmm, jury is still out on them and the fault. They have traced it to a zero voltage at the drivers side door control module and had the door apart. This would make sense in terms of waking the car up. Note it is not the door handle sensors, it's apparently the door module. They have had it 4 days so far, hurry doesn't seem to be in their vocab. They haven't seen or heard anything like this before. I'll let you know how I get on...

The door module was a red herring. It was not working but not the cause of the car's insomnia/batter drain.The car returned just after new year, not fixed but problem identified as the diagnostic module 4Ho907468F. I have been running the car with this module disabled by pulling the fuse and the car has been fine. I have located a second hand one and it will be fitted when I get the chance. All that work and it turns out to be the diagnostic module not allowing the car to sleep. Time will tell whether the replacement is a full fix. Thought I'd keep this updated as there is nothing anywhere on the internet about a faulty diagnostic module or this type of battery drain.

Thanks that's very useful to know - not heard about that particular issue anywhere yet but a lot of this type of issue will no doubt come out of the woodwork over coming years!