Check behind the wall lining in the boot. Remove the boot carpet then pull out the the side wall lining and you'll notice there are a couple of holes in the body which ford have covered with black gaffa tape. This become loose over time and comes off. This then let's water seep into the bottom of the boot area filling the spare wheel well along with wetting the boot carpet. This can run forwards or backwards depending on which way you park your car on a slope. I pulled back the lining on both sides then filled the holes with sealant.
Just an update if anyone is interested the water leak in the boot does indeed come via the air vents and small hole behind the bumper. I attempted to remove the whole rear bumper to gain access to the vents then realised it can be reached if you lie beneath the bumper and reach up until you can feel the vents. If you give the edges of the vents a goid clean with a rag etc, and apply liberal amounts of flexible sealant to your fingers you can indeed seal all around the vents
( take your time and check whist doing this)
You can also reach the area where Ford have covered a hole with black tape and cover that with sealant also. I did both sides and 2 weeks on and still my boot is dry. Unfortunately the rear passenger footwear which the water had run into is taking a little longer to dry out but is getting better every day.
So crawl under the rear bumper and get some sealant around the edges of the vents and the small hole. 1 hour of a job.