Hi AudiTech4, been away for ten days, but first drive on return and tried to rev engine after it had been switched off. Rev'ed beautifully! till I took foot off brake!

 

If I had to guess, which I might as well because nothing else is out there, it sounds like your brake lights (or something similar that should work without the key on but is in someway connected to the brakes) are wired into your ignition switch or are wired wrong and are keeping the switch fooled in the on position. You have not messed with the wiring in your car have you? All electronics work while it is "off" too? My step dad purposely wired our van to stay running if the headlights were on, I guess as a reminder to turn off the headlights, so I know it can be done. The key on/off position is just controlling whether the voltage to run your car can pass the ignition switch or not, so it kind of appears like the brakes are allowing that voltage to bypass. What kind of custom equipment? Glow in the dark pedals, new stereo stuff, anything installed? Due to the irregularity, I would say you are looking for a frayed wire or damaged wire insulation (perhaps even from rubbing).

 

Dan, Thanks for your ideas!
Car is standard factory issue, no modifications, no customisation.
No, I haven't messed with the wiring and all electronics work when car is "off".
Your thoughts on possible damaged wiring and irregularity have me wondering whether the steering wheel position when I switch off may be causing the intermittent effect.
I will look for wiring issues and I'll test the steering theory.
Will keep you all posted.

 

I know you say the dealer cant reproduce this

But have you ever tried to do it your self while at the dealer with the Service manager or advisor or tech

 

AudiTech4, yes. It's random, and I have stood with the tech while he tried, and then I tried.
When, if, it gets more predictable, I'll take it back to them.

 

Take it to a local mechanic that is familiar with imports, tell him to by pass the brake light switch and try again, I agree with Dan, it could be something related with the brake switch.