Hogweed

I know people (like me) often search through the topics when they have similar problems - so, if anybody's reading this years later, I have tentatively come to the conclusion after all the deliberation ove door switches, boot switches etc etc etc that the main culprit was two faulty LION batteries.

When I got the first one replaced under warranty, the alarm problem went away for a few weeks, then returned. A the same time, the car got harder to start when it had been sitting for a few days.

I got the battery replaced again - no problems since, and the car starts easily after even a week or two.

Thanks again for everybody's help.