The exit poll is believable. For it to be right, two key and unexpected things seem to have happened.
First, the Tories have held onto far more seats in England than we thought they would. Rather than losing more than thirty to Labour, they may have lost as few as a dozen (or even less). They may have even won a few seats from Labour, but we are guessing that there has been a net loss to Labour of around ten. That would mean the Tory seat total rises from the low 270s, as we had expected, into the high 290s.
But the exit poll says the Tories have won 316 seats. Who are the other 15-20 unexpected wins coming from? The Lib Dems. That is the second shock. They seem to have lost many more seats to the Tories than we expected. The party’s supposed ‘incumbency effect‘, with popular local MPs overcoming the Lib Dems’ national collapse, doesn’t seem to have materialised.