Ooo an automatic as well, yeah I wouldn't be surprised if it's gone through another battery. 

If you can't find any sort of drain on it and you keep having weird electrical issues then I'd look at changing that first

Follow-up to my follow-up:

A strong email to the Dealership's Technical Director forced my local one to step into action!

They performed a proper battery-drain test and found that it was losing charge at an unacceptable rate (funny that, as that is precisely what I was telling them!).

Anyway the outcome seems to have corrected the problem - a module (called a TCU - Telematics Control Unit) was faulty and was trying to access wifi continuously* in order to upgrade system software, draining the battery at an amperage of 1.4A. Replacing the module reduced this to 0.01A after 30 minutes of switiching the ignition off!

They also replaced my battery, one of the things I insisted on in my email! So, after 5 -6 days of not driving the car, today it started normally and the stop/start engine function worked fine too.

Fingers crossed, but it looks as though the problem has been finally fixed.

   * I happened to include in my email the fact that I was getting a message on the console almost every time I started the car that software was being updated - apparently I should not have been receiving this message (only useful in the USA, I was told) and that lead them to looking at the TCU

Very well done Tcal, you should get a medal !! Getting a dealership to actually do something other than come with a new excuse is a major result 🏅

Good to see confirmation that this was NOT a battery problem, and the current draw got down to around 10mA once everything went to sleep. That's more like it.