"They could not (and would not even if they could) legally demand a second vote. They can certainly place conditions on any extension (and will) "

Yes, they can't dictate but they can wrap it up in words that don't say it but mean it. Two years, providing a comprehensive re-think is undertaken, would do nicely and has already been hinted at.

But I've lost faith that there are enough British people who will voter Remain in either a General Election or another referendum.