The opinion polls are - let's be frank - all over the place.

The Conservatives are still ahead in the latest batch but their advantage ranges from 1 to 12 points.

This means we are either looking at a hung Parliament or a thumping Conservative majority, or something inbetween.

The problem, says Ben Lauderdale, of the London School of Economics, who helped create the YouGov model which had the Tories as low as 18 seats short of a majority, is that pollsters can't agree on which voters will turn up on the day.

"None of us are stupid, none of us are crazy, we all may be wrong in the end or some of us may be wrong, but it's just a difficult problem," he says.

The polling companies changed the way they work things out after failing to predict the 2015 election.

They got it wrong because their polls were biased towards people who normally vote.

But they don't know how many of the politically disengaged non-voters who unexpectedly turned out in their millions to vote for Brexit will bother to vote in the general election.

Also, YouGov believes that if younger voters turn out in big numbers on Thursday, then Theresa May could win a much smaller majority than initially predicted or even lose.