'Radio wave interference' is often blamed for unexplained problems with central locking and imobilisers. a recent example that made national news was:

news.bbc.co.uk/1/hi/england/cumbria/8545104.stm

However, I would have thought that the recovery organisations would be aware of any blackspots by now.

The fact that the aa had to recover the car is 3rd party evidence that the non-start problem really existed, so the dealer should investigate. If they feel the dealer is not handling the issue to their satisfaction, then try another.

I do not know the Megane, but HJ's Review for the previous model mentions:

"Keycard failsafe requires driver to press clutch before starting with card, but electrical cable for this can dangle into footwell and get snapped."

Does the new Megane require the clutch to be depressed also?

I was told once by a patrolman that as the car manufacturers' roadside assistance schemes were handled by different companies, this meant that a particular motoring organisation either dealt with the majority, or else very few, issues with newish cars of a given make. Should your parents be unfortunate in having further problems, it might be worth checking to see who handles Renault's scheme and joining that, if it isn't the aa.

Hope it gets sorted quickly.