Thanks for the information guys, especially about the dealer in the Lake district.
Martins, ( i.e Basingtoke ) took it in this morning at short notice, and have diagnosed a faulty light cluster. It's the strip one across the top of the back window. Only half of it was working and my wife did not realise this was the issue, until it briefly fully illuminated while she was watching it this morning for me.
I was in the car of course and did not see this on the weekend.
Should get it fixed tomorrow, if the part comes in on time.
I will do the write up for Martins later in the week and give a full report of their service when the job is finished.