I decided to spread my risk and ordered 'essays' from 3 sources:
**********

UKEssays
MadPapers
Also, I signed up to an online plagiarism / style checking service to validate the materials produced.
Results
******* delivered on time and to the quality ordered
Ukessays were c.50% reliable - they managed to (more or less) sort the issues with one essay produced, but the final one was originally rubbish, then with a 'rewrite' from a different author was mostly plagiarised from web sources.
MadPapers was completely random, again I had to have extensive rewrites and was still not satisfied at the end.
As I was only using the material for reference, the plagiarism wasn't damaging, but was clearly not what they promised.
Overall, my experience was slightly better than I expected, but I would probably not use at least two of the providers again.