Britain is gripped by political crisis. We have a prime minister bent on taking Britain out of the EU in just over a month, even if it means crashing out with no deal, with dreadful consequences for jobs and growth, for regional inequalities and for the union. Lacking any democratic mandate, Boris Johnson has shut down parliament for five weeks in an attempt to stop MPs from blocking him, a move whose legality the supreme court will rule on this week. Yet the Labour party is heading into its conference this weekend riven by splits over Brexit and sectarian attempts by Jeremy Corbyn’s allies to scrap the position of deputy leader.

It represents a breathtaking failure of leadership by Corbyn. Never has Britain been in such desperate need of a leader of the opposition who can take on a prime minister who appears prepared to ride roughshod over the rule of law and who has shown such rank disregard for our democratically elected representatives. Yet Labour seems determined to show voters that it, too, is a hopelessly divided party that cannot reach consensus on its internal party structures, let alone a clear position on Brexit or a vision for the country.

Following an overwhelming backlash, a motion to abolish the position of Labour deputy leader, currently held by Tom Watson, was hastily withdrawn. But the damage is done. Corbyn looks like a leader more interested in quelling internal dissent than winning a general election. It is yet another sign that, like the Conservatives, Labour is cementing its move towards the political fringe, unable to accommodate a broad church of perspectives that includes a lifelong social democrat such as Watson, who was directly elected by Labour members and can legitimately claim to speak for many in his criticisms of the leadership over Brexit and its abject failure to tackle the antisemitism in its ranks.

Labour will pay the price at the polls. Despite Johnson’s relative unpopularity, Corbyn lags far behind. New polling for the Observer this weekend puts the Tories 15 points ahead of Labour. Labour’s unclear Brexit position is undoubtedly part of the explanation: for the first time, of those who voted Remain in 2016, as many say they would vote Liberal Democrat as Labour. Seven in 10 say Labour’s Brexit position is unclear.

Little wonder. While Labour has gradually moved to adopt a referendum on any Brexit deal, its stance is still one of tortuous prevarication. The official position is that it would negotiate its own Brexit deal, then decide its position on Brexit, and then put the deal to a referendum. Corbyn allies argue that acting as a “neutral arbiter” would allow him to unite a divided country.

But a man who wants to be prime minister must come clean with voters on where he stands on the most important question this country has faced in decades. Three years of talks have only highlighted the fact that any form of Brexit involves painful trade-offs. A close relationship with the EU will limit the economic pain but will involve signing up to free movement of people and giving up our say in the making of the rules we will have to continue to abide by. A hard Brexit with some form of backstop will have a worse impact on growth and will either require customs checks in the Irish Sea or limitations on the UK’s ability to do trade deals with the rest of the world (which the government’s own analysis says could never compensate for the loss of trade with our closest trading partner). The options are clear: Remain, a soft Brexit, a hard Brexit or no deal. There is no excuse for Corbyn to be unclear about which he would campaign for in any referendum.

Labour believes it is politically expedient to avoid this, but today’s Observer poll shows its fudge is fooling no one: the party is losing support among voters who voted Remain and those who voted Leave in 2016. Corbyn is right that there are pressing issues other than Brexit that must be addressed. But Labour will never get the space to be heard on them if its leader cannot answer the question: where do you stand on Brexit?

There are parallels with David Cameron’s disastrous approach to the 2016 referendum. Cameron spent months of his premiership trashing the EU and exaggerating its weaknesses. He arrogantly believed he could convince voters by switching tack just weeks before the referendum. His lack of leadership – and Corbyn’s own half-heartedness in campaigning for Remain – left a vacuum that was filled by voices such as Nigel Farage, Johnson and Michael Gove.

As Labour prevaricates, history is repeating itself: Johnson’s insidious “parliament versus the people” narrative is getting traction as Labour is hopelessly dominated by internal struggles. Corbyn cannot unite the country by avoiding the question. Labour must make clear it would campaign for Remain, because any form of Brexit would make achieving its agenda of better public services, greater equality and stronger regional economies immeasurably harder. Those Labour MPs naively toying with backing Johnson to deliver a hard Brexit must think again: all they will do is bolster his premiership and provide further succour for the deregulatory, low-tax agenda of the Conservative right.

In threatening to thwart the will of parliament, Johnson has launched an assault on representative democracy. Only Labour can stop him. It would be a tragedy if, instead of taking the fight to one of the worst prime ministers this country has seen, it consumed itself in bitter conflict. The whole country would pay the price.