So, we (I) think we have found the issue.
Firstly the TPM chip. Turns out there is a BIOS setting to enable it that nobody thought to check...
But that's the minor issue.
The major issue is the constant blue screening. It dies with the error CRITICAL_PROCESS_FAILED. It doesn't store any memory dumps or anything so no blue screen analyser tools help.
With some digging we have found a few other people with this same issue and it turns out they all have something in common, they have reinstalled Windows.
Initial thoughts point at reinstalling Windows using the AHCI mode for the SSD as the cause, with the suggestion being to swap to RAID mode. However, RAID mode still dies, and if you set it to RAID in the BIOS and then try a clean install the installer won't see the disk.
So what we have determined is that the stock Windows image that comes preinatalled on the latop from Dell has something in it (drivers maybe?) that aren't in a clean install. My laptop was formatted the moment it arrived and Windows 10 Enterprise installed.
So, simple then, revert to the Dell image from the recovery partition. Ah, no, that's gone, formatted off when the Enterprise version was installed!
Ok then, use the recovery media. What recovery media? Oh thats right Dell don't ship that any more and you have to pay extra.
Order it then? No, that wont work either as this laptop was bought with a Windows Home license as we knew it would be thrown away anyway!
So I've got an XPS 15 that doesn't work because we formatted it, that we can't return to the Dell image, and wouldn't work (domain access) even if we could as its Windows Home!
So it's going back, and a replacement has been ordered that comes with Windows Pro that we then wont touch other than attaching it to the domain. Annoyingly that's another 2 to 3 week wait for delivery.