It’s my job to predict elections, but this four-party fight will mean everything is up for grabs

Many seats might well be won with no more than a third of the vote. Much will depend on whose vote is the more efficiently distributed and how tactical voting is used

It looks likely that at some point between now and Christmas, though maybe only after Halloween, Britain will hold its third election in little more than four years. It would be the first time the country has gone to the polls with such frequency since the early 1970s. Our politics is evidently in an unusually febrile state – the outcome of which is even more difficult to anticipate than usual.

Traditionally, British elections were dominated by two parties, the Conservatives and Labour. Only the Liberals, and more recently the Liberal Democrats, presented much in the way of a third-party challenge. Correctly forecasting the outcome of an election essentially meant working out which of the two big parties was going to be the more popular, with just an occasional glance at what the Liberal Democrats might achieve.

True, in 2015, the Liberal Democrats’ status as principal third-party challenger was usurped by Ukip in England and Wales and, even more spectacularly, north of the border by the SNP. But if the character of the challenge had changed, in any one part of Britain, there was still only one significant third player that merited any serious consideration.

But now in England and Wales it looks as though not one, but two third parties could secure a significant share of the vote.

The Liberal Democrats are back in business after years of electoral famine in the wake of the 2010-15 coalition. At the same time, while the name of the party may have changed, the Brexit Party now occupies much the same position on the electoral landscape that Ukip did in 2015. So, individually neither challenge is new, but never before have both been in evidence at the same time.

The advent of four-party politics creates new areas of uncertainty. It means that many seats might well be won with no more than a third of the vote. Much will depend on whose vote is the more efficiently distributed. In such an environment, more voters are likely to face the dilemma of whether to vote for the party they most prefer, or to vote tactically for whoever locally seems best able to defeat the party they like least.

Even the parties themselves may decide it is worth their while to try and game the system by entering into electoral pacts in some seats – as both Nigel Farage and some pro-EU campaigners have been suggesting.

Brexit is, of course, the immediate reason why England and Wales now have four-party politics. The Liberal Democrat revival has been founded on winning over Remain voters attracted by the party’s insistence that a second referendum should be held in the expectation that this would reverse the decision to leave the EU. For the time being, at least, the party has left behind its days as the “centre party” of British politics.

Meanwhile, the Brexit Party has become the vehicle through which many Leave voters have opted to express their frustration with the UK’s failure so far to leave the EU.

Both those parties have been able to articulate a clear stance on Brexit that has, until now at least, eluded both the Conservatives and Labour. The issue cuts across the division between “left” and “right” that provides the lifeblood and motivation for politicians and supporters of our two largest parties. All parties are coalitions, of course, and this environment makes it difficult for either to keep theirs together.

In any election this year Brexit is likely to be centre stage to a much greater extent than in 2017. Even then, it made a difference to how people voted. The Conservative Party lost ground among Remainers while advancing among Leavers. That in turn had a substantial impact on the geography of its vote, as illustrated by the party’s success in the traditional Labour heartland seat of Mansfield while losing leafy Kensington and Chelsea.

Under our first-past-the-post electoral system, further changes in the geography of party support could make a big difference to how votes get translated into seats.

Brexit could yet have other unpredictable consequences too. As a result of last week’s split in Conservative ranks, a significant number of “independent Conservatives” may stand, potentially fracturing the Conservative vote in their constituency. The intensity of the debate about Europe could bring significantly more voters to the polls. Meanwhile, the Liberal Democrats appear to be hoovering up other parties’ former MPs at a record rate, potentially boosting their electoral chances.

All in all, not the easiest time to be a political forecaster!

John Curtice is a professor of politics at Strathclyde University and a senior research fellow at the NatCen Social Research and The UK in a Changing Europe initiative