Having been supplied with a replacement one way valve for the rear screen washer by Clive, fitting that and adjusting the nozzle so it sprayed onto the rear window and not the ground behind the car, I was able to say that absolutely everything worked as it should on my car. After 5 days of this almost unheard of state, the book symbol came up on the HEVAC. Nanocom reported a compressor clutch fault and setting the HEVAC to Lo on both sides and noting that the compressor clutch didn't engage I concluded that there was indeed a fault that didn't have an obscure description. Did a bit of checking and found that the reason it wasn't engaging was no continuity through the trinary switch. Reason for that was that it has no refrigerant pressure in it.....
I did notice that although the AC was working last summer, it seemed a bit feeble so it looks like I now need to get it re-gassed. Although the reason for it losing pressure could be down to a minor leak somewhere (it was last gassed about 2 summers ago) so I think this is going to get a bit more involved. Then, to add insult to injury, last night I switched the lights on, the dash beeped and the message centre came up with RH sidelight failed. So from no faults I've got two in the space of two days!