The political world has changed and it is hard – not just practically, but emotionally – to keep up.

Last week, I pulled off my shelf a book of counterfactuals by Iain Dale and Duncan Brack.  It is entitled Prime Minister Boris and other things that never happened. 

Written in 2011, the relevant chapter runs through a series of increasingly elaborate scenarios that lead to the collapse of the Cameron government and Boris’ rise to the top. It is, of course, a joke: it could never happen.

The speed of change from the impossible to the improbable, to the merely unlikely and perhaps inevitable, has accelerated in recent weeks.  Just over two months ago, a Liberal Democrat party stuck for the best part of a decade on around eight percent in the polls seemed set to slug it out for its very survival with Change UK and possibly the Greens.

Today, the party is consistently polling between 17 and 23 per cent and, indeed, has twice topped national Westminster intention opinion polls since the European elections.  With the parallel decline in support for the Conservatives and Labour, and the creaming off of substantial leave votes from both to the Brexit party, the latest analysts predict anywhere between 75 and 105 seats for the Lib Dems from their current position.

A four-way battle, however, opens up the possibility that very moderate further swings could quickly see the Lib Dems gaining upwards of 200 seats and indeed becoming the largest party in Westminster.

Pure Lib Dem fantasy?  Well, increasingly, the talk in Westminster is of an Autumn election to underpin a Boris premiership and see off Farage.  To achieve this, Boris would have no choice but to lead the Conservatives firmly towards a no deal position and, with the Amber Rudds of his party now willing to support such a policy, who in practice would stop him?

But such a tack would paint the Conservatives firmly into a corner.  Analysts are now telling us that increasingly the political divide in British politics is no longer party allegiance or class, but leave or remain: our positions on Brexit have become our political identities.

Why is this?  Surely not because we feel passionate one way or another about the European Union, an issue which – let’s not forget – for most of the last fifty years has failed to make it into the top ten of voter priorities at general elections.

Instead, remain or leave have become proxies for the type of society in which we want to live – open or closed – nationalist or internationalist, free-market or protectionist, inclusive or insular.   And these values have very largely replaced traditional party or class allegiances in identify voting patterns.

A Boris-led Conservative party would be choosing to limit its potential electoral appeal to a group not much greater than a third of the electorate, territory over which it would then be forced fight with the Brexit party.

Labour looks in real trouble, with a membership that identifies as ‘open’ but a leadership which is ‘closed’. and unable to move on from a debate around anti-Semitism which speaks to the uncomfortable latter position.

In contrast, the Lib Dem surge over recent weeks derives from its now unchallengeable claim to be the party of open Britain.  While in maybe a dozen seats in England, they might have to compete for the position with independents, Greens and the remnants of Change UK (and the electoral arithmetic is different in Scotland and Wales), elsewhere the Lib Dems will have a free run for the open vote, a vote that now accounts for upwards of 35 per cent of the British electorate.

In a four-way battle that is more than enough to win an outright majority.

Do I think that that will happen?  It is far from inevitable, but it has also moved a long way along that scale from impossible.   The changes that have taken place in Britain over the last decade – and accelerated since the referendum – are so fundamental and transformative to British politics that the past is no longer a reliable guide to the future.

For the first time, going into an election the Lib Dems ‘own’ an issue that is a proven vote winner.

For the first time, the previously powerful wasted vote message with four parties polling around the same looks massively diminished.

For the first time, Labour and the Conservatives look set to enter the election with leaders who are both decisively outpolled by ‘neither’ in the choice of best PM.

So it is time for a new mindset.

First, the Lib Dems need to believe that they are competing to win.  They need a programme for government that may begin with revoking article 50 but will need to underpin an open and inclusive society through policies that address the causes of Brexit in the first place.  And that will take real radicalism.

Second, the media needs to start treating seriously the prospect of a Lib Dem victory.  This is not about who holds the balance of power.  This is about who could realistically be the next Government of this country.  Is PM Jo Swinson really that much less believable than Prime Minister Corbyn, or Boris?

And so journalists will no doubt also want to start subjecting the Lib Dems to proper scrutiny, together of course with the other new alternative, the Brexit party.

Third, the pollsters have a responsibility to start testing how the public might actual view the prospect of Jo Swinson or Ed Davey as PM as compared to the alternatives – as former government ministers they have more experience than Corbyn and having never been sacked, more staying power than Johnson.  They might note that the inclusion of Jo Swinson as an alternative to Johnson or Corbyn in a recent YouGov poll put her party into first place.

And finally, those in business and elsewhere who believe that Brexit represents an existential threat to the UK, better be ready not to choose between the lesser of two evils but to put their money where their mouths are: a Lib Dem party funded on an almost level playing field with the Tories and Labour could be the potent force that business wanted all along.

If Mssrs Brack and Dale are dusting off a new set of counterfactuals, I’d advise them to avoid the story of Prime Minster Swinson in the list of things that could never, ever happen.