I managed to trace it back to a mis-inserted fuse. When I originally checked the fuse it was out in the wild, with rain wind, and fuse box being on the offside, meant I was in danger from oncoming traffic and rain getting on the electrics, so I took the fuse out and checked it inside the car then got out to put it back in the fuse box. I thought I'd put in the right place, but as a double check I used a count-back from the populated end of the fuses, shown on the card clipped to the fuse box cover panel.
When I decided to check the circuitry back to the ECU, I figured the fuse box was an easy point to eliminate. And when I removed the cover I had a JDLR moment (just doesn't look right), so I did the count back again but this time spotted and empty fuse space right in the hinge corner where it's difficult to see. Also the row of fuses above doesn't line up to the card diagram. So my original positioning with a single space form the next fuse was correct. As soon as I turned the ignition key, I could hear the pump run, and saw the voltage drop on the accessory socket, so I didn't bother firing it up, until I had enough time to run it up to working temperature, and make sure there were no more surprises.
I've now marked on the card where the fuses are actually present. I've also made a blow-up and mirror image of the fuse box, from the tiny handbook pic, which is only 36mm high, too tiny to see clearly, and a mirror image of reality. Essentially the manual pic and card, are just the RH drive car images, just chucked in regardless. Wonder if the LH drive Audi owners manual is similarly slipshod (if they do a model with that fuse box position)?
I recommend owners with this fuse box to mark the card *as populated* and take a pic of the box vs the roadside alternative faff.
1) card as suppled. 2) card now marked where populated. 3 actual fuse box.