That's a bit extended, basing results in 308 constituencies based on 3 seats is ... you know
True, but it's what the BBC did after every by-election between 1992 and 1996 (most famously in Dudley West where the swing to Lab was so big, no Conservative MP's would have been elected so they had to add a Conservative MP for the computer model to work!)
I think they did it before 92 as well... although maybe only where there was a major swing. I recall reading that for the 86 Fulham by-election, it showed Labour one seat short of a majority.
Re Harry - what's the distribution just for Quebec?