I wouldn't call the Brexit referendum because I thought it would be very close. I also thought Trump might win and was ridiculed for not being convinced that Labour would win in '92.
My gut tells me that Labour will win, but that they won't have the massive majority that recent polling suggests. I think they'll have an overall majority in the region of 30-50, and will be surprised (but delighted!) if they get a majority of more than 100. I also think that, while Reform will take votes from the Tories, they'll also take from Labour, but hopefully not to the same degree.
I'm hopeful that voters are coming round to the idea of voting tactically. I live in a Lib/Con marginal, and loads of Labour voters here vote tactically. I fully expect to see the Liberals win some seats in the south for the first time in ages because of that. If LD voters in Lab/Con marginals are prepared to do the same, that will make a massive difference. For those considering it, there is a website, tactical.vote.co.uk, which gives the best option for each constituency.
There are 2 big unknowns though. There have been lots of significant changes to boundaries since the last election, and it's hard to predict the impact of the Reform party. I think Reform will take votes from Labour as well as from the Tories. I think (and hope) that they won't win any seats, but I think they may have a significant effect on outcomes in some areas.