For some unknown reason I appear to be collecting water in my spare wheel well. The mats above are not damp and the seals look good.

Has an had something similar, what is the solution?

More than likely coming through from the rear light clusters - worth removing them and seeing if the gaskets have been letting water past them.
If so, and before refitting it would be prudent to smear some silicone on the gaskets before refitting them

Also, it could be leaking through the tailgate seals or even rear screen washer hose is damaged and allowing water to drip into the boot area.

The ultimate way to resolve the issue is to run a Smoke Generator inside the boot area and see where it comes out from

eBay link to a Smoke Generator: Smoke Generator