When Labour MPs and activists campaigned during the general election, voters repeatedly told them, “We don’t know what you stand for.” The party had assembled more policies than any opposition in recent history but lacked a unifying theme. As the former shadow business secretary Chuka Umunna later told me, “People didn’t know what we stood for because we kept changing our bloody message every bloody month.” The party veered from “responsible capitalism” to “one nation”, to “the cost-of-living crisis”, to “a better plan, a better future”.

In contrast, the Conservatives, as they never ceased to remind voters, had a “long-term economic plan”. Lynton Crosby, the Tories’ campaign manager, credited this discipline with delivering them a parliamentary majority. “Message is everything in politics,” he concluded.

When Jeremy Corbyn won the Labour leadership, his supporters expressed the hope that he would give his party comparable definition. The left-winger triumphed on an unambiguous policy platform: he opposed austerity, military intervention, Trident renewal and tuition fees. But in the two months since then, Labour’s message has been more confused than ever. Shadow ministers have contradicted each other to the point where collective responsibility has appeared non-existent.

It is over the nuclear question that the fracture has been greatest but divisions have not been confined to this totemic issue. Andy Burnham’s warm welcome for Theresa May’s draft Investigatory Powers Bill was undermined by briefings that Corbyn took a more critical view. In a letter to May a few days later, released to the New Statesman, the shadow home secretary demanded far stronger safeguards. When Corbyn called for a review of UK air strikes against Isis in Iraq, a spokesman for Hilary Benn swiftly replied that the shadow foreign secretary continued to support the stance that the party’s MPs “overwhelmingly voted” for. The question of who speaks for Labour has become ever more insistent and the answer ever less clear.

A tipping point was reached when the shadow defence secretary, Maria Eagle, endorsed the criticism by Nicholas Houghton, the head of the armed forces, of Corbyn’s pledge never to use nuclear weapons (“It would worry me if that thought was translated into power,” Houghton said). This finally prompted the Labour leader to “lay down the law”, in the words of one shadow cabinet member, at a meeting of his team on 10 November. He told them that statements should be cleared with his office and spoke of the value of collective responsibility.

Ed Miliband also struggled to impose discipline after winning the leadership in 2010. As his victory had been achieved without the support of party members and MPs, he was treated as illegitimate by some colleagues. For Corbyn, despite his overwhelming mandate, the challenge is of a different order. Because of his rebellious record (voting against the party whip 534 times since 1997) and perceived unelectability (“The public will think Labour has given up on ever being a government again,” said Burnham before the result), his authority is far weaker.

Rather than Corbyn’s word, it is Labour’s 2015 manifesto that is treated as sacrosanct. Unless the party’s positions are formally changed though its conference and National Policy Forum, shadow cabinet members will continue to advocate stances such as Trident renewal (and some would resign rather than cease to do so).

Shortly after the Labour leader formed his first shadow cabinet, Diane Abbott complained to MPs about the lack of Corbyn supporters included. Just three, including Abbott, voted for him (the others being the shadow chancellor, John McDonnell, and the shadow communities secretary, Jon Trickett). Should Corbyn’s attempt to impose discipline fail, the pressure to include more true believers will increase. One supporter told me that a reshuffle after next May’s elections was “essential”.

It is these contests – in Scotland, Wales, London and metropolitan boroughs – that all sides await as a clarifying moment. Some MPs predict that Corbyn will suffer what one describes as an “early collision with the electorate” and face a formal leadership challenge. But were he to be challenged, many believe that he would win by an even larger margin. MPs do not fear deselection by activists but nor do they entirely dismiss the possibility. At a recent Nottingham meeting of Momentum, the grass-roots group established by Corbyn supporters, the former shadow chancellor Chris Leslie was identified as a target.

The case of Andrew Fisher, the aide suspended from Labour for allegedly backing rival candidates in May, has become a proxy war. “All the MPs pushing the campaign against Fisher are people who want to get rid of Jeremy,” Ken Livingstone, a member of the National Executive Committee, which will rule on the dispute, told me. “It’s no good all this lot saying we can never win with Jeremy when they’re doing everything to undermine any chance of winning the next election by being divisive.” The support given to Fisher by Corbyn and McDonnell despite his suspension by the party’s general secretary, Iain McNicol, again prompts the question: who speaks for Labour?

For Corbyn, the task is to transcend the unending stream of process stories and define his leadership on his own terms. MPs speak with surprise of the absence of a set-piece speech distilling his mission. Corbyn can point to political victories in his opening months: the Lords defeat of tax-credit cuts, the cancellation of the government’s Saudi prison contract and the absence of a vote on military action in Syria. But he has lacked an overarching theme. Unless Labour has a message, it will never have discipline.