As the original poster, thought I'd update on what I now think the
problem with fuse 34 constantly blowing was.
I'd eliminated the 12v accessory sockets by moving their fuse to the 'always on' position.
Still the fuse 34 blew leaving me with no photochromic rear-view mirror although the other items listed in the owner's manual (reversing switch and 'clima sensor' whatever those were) were a mystery, especially as my reversing light still worked.
Then a few days ago, I started to hear the sound of a worn bearing or some such on tick-over. Sounded like one of the belt-driven ancillaries like the water pump, alternator or a/c compressor. Took it back under warranty and the fault was diagnosed as a 'faulty pulley' to the a/c compressor, i.e the pulley with a built-in magnetic clutch which apparently looked burned-out.
I then got to wondering, especially as the
garage had also reinstated fuse 34 without comment if the 'clima sensor' is the switch for this clutch. Makes you wonder, as it's now all working again.
Faulty phone charger? My arse!
p.s I the mean time I'd gone to the trouble of downloading an entire Mk3
service manual, all 3118 (yes, you did read that right) pages of it in pdf format. Don't bother - there's no index and worse still , NO wiring diagrams (I know I scanned through all 3118 pages of it!)