Right, so the new battery went flat in 5 days during which I did two 23 mile trips. I'm fairly sure that the lights, wiper, hazards and heated windscreen are all off and not drawing any current. The Parrot seems to only come on with the key switch and I have a Power Box plugged in but I've had that since January and it's not caused a problem. Something must be drawing current from the 12v battery when parked in the shed (sorry - Twizy accommodation).
There is a click/clunk when I reconnect the battery and I wonder if 12v is used to hold open a switch to the traction battery and then closes when I switch on, in which case something must have changed because I haven't had this problem before in a year of use.
A wiring diagram would be useful but as the fuse page in the manual is as much use as a chocolate oven glove I don't hold out much hope that Renault have made that available.
If there isn't a solution I'll just use @ALEXAKOS trick of wiring in a socket for a 12v charger. and keep it topped up.