LONDON — Britain's next prime minister is in the process of being chosen by around 160,000 Conservative Party members — a self-selecting "selectorate" that is predominantly over 55, relatively wealthy, and, needless to say, not representative of the country.

When their chosen leader drags himself out of that toxic sludge, he’s in for a shock.

Not only will he face a Conservative Party irrevocably divided at the grassroots level and a country poised to wreak revenge for the Brexit shambles at the first opportunity, but he will also face an anti-Brexit front more united than ever before.

Parties such as the Liberal Democrats, the Greens and Plaid Cymru are starting to work together for the greater good. We're putting aside our differences and focusing on doing everything collectively to stop a no-deal Brexit — and, indeed, to stop Brexit altogether.

In the upcoming Brecon and Radnorshire by-election, Welsh party Plaid Cymru has endorsed the Liberal Democrats because we offer the clearest chance of victory for pro-European voters. The Green Party has also decided to stand aside. That means anyone wanting to elect a candidate who is committed to stopping Brexit will be voting for the Lib Dems' Jane Dodds, maximizing the chances of taking back this Welsh seat from the anti-European Tories.

The looming disaster of an ill-conceived and appallingly executed European exit should have brought us together sooner.

It's hard to overstate the significance of this alliance. The decision is a beacon of political pragmatism and principle in the current fog of cross-party rancor and offers a roadmap for building an effective anti-Brexit front that can save our country from lurching toward disaster.

In votes to come — for instance in a snap general election — it may not be the Greens and Plaid whose name is left off the ballot paper but my own party’s, where other pro-EU parties stand a better chance of winning against Brexiteers.

The looming disaster of an ill-conceived and appallingly executed European exit should have brought us together sooner. These are extraordinary days in politics, which threaten the very future of our United Kingdom and the institutions we have fought to build and protect.

Faced with these challenges, we must realize collaboration is not a dirty word and seize this new momentum. Those of us in pro-European, internationalist parties can show how collaborative politics should be conducted in the 21st century — and save this country from destroying itself in the process.

The current turmoil in the Conservative and Labour parties may bring more MPs to join the Lib Dems; but it may also produce committed Conservatives and socialists who nonetheless wish to stand in defiance of their parties as part of a broad Remain alliance.

Brexit is the single biggest issue our country has faced in a generation ... if we can’t come together for the greater good at a time like this, we never can.

The campaign group Best For Britain, under the leadership of Naomi Smith, continues to be inundated by people signing up to oppose Brexit in all its forms. They are demanding that politicians find ways of working together to break the Brexit impasse — more than 80,000 have now signed their petition calling for parties to work together.

Like them, I don't want to spend the rest of my life in a broken Britain, wondering what if we had reached across the political aisle to form an alliance and fight for our nation's future?

Brexit is the single biggest issue our country has faced in a generation, if not longer — if we can’t come together for the greater good at a time like this, we never can.

The alliance we and our partners formed for the Brecon and Radnorshire by-election should become a blueprint not just for politicians, but for voters too.

By reaching out to our fellow pro-Europeans, we are showing voters what can be achieved when traditional party loyalty is set aside in order to make a significant difference at the ballot box.

Until we get equal votes by ditching first-past-the-post for a more proportionate system, we will need to rely on such tactics — particularly when regressive parties are organizing against us.

Faced with the moronic machismo and isolationism of the Conservative leadership candidates when it comes to Brexit, the anti-Brexit camp's only chance to keep the country from sliding into disaster is to set aside our differences and work together.

Vince Cable is leader of the U.K. Liberal Democrats.