At a recent shadow cabinet meeting, John McDonnell declared that Labour had become a “government in exile”. It is this status that all oppositions seek. Those that achieve it typically enjoy large gains in local elections. In 1995, Tony Blair, the last Labour leader to move from exile to power, won an additional 1,807 councillors. Even inadequate oppositions advance almost by default. Michael Foot, Iain Duncan Smith and Ed Miliband all enjoyed local success before national failure. The last time that an opposition lost seats in a non-general-election year was in 1985, when the SDP-Liberal Alliance surged.

On 5 May, Labour is forecast to break this 31-year record. Based on current polling, John Curtice, the doyen of British psephology, predicts that the party will lose 170 councillors. If so, Labour will not be a “government in exile” but an opposition at home. Sources report that the party is shedding support in the south of England.

Jeremy Corbyn’s allies have long emphasised that the relevant councils were last fought in 2012, the year of George Osborne’s “omnishambles” Budget (which helped Miliband gain 823 seats). Labour MPs noted that this trajectory still ended in defeat in 2015 – but the point was taken.

Yet, in recent months, the government has endured a repeat of its 2012 debacle. Like most sequels, it was gorier than the original. The Chancellor’s March Budget unravelled faster than any in recent history. Soon afterwards, Iain Duncan Smith resigned as work and pensions secretary and accused the government of betraying the poor. David Cameron was forced to concede that he had benefited from his father’s offshore trust. Tory MPs revolted against the forced “academisation” of schools. Junior doctors walked out over new employment terms. Meanwhile, pro- and anti-EU Tories traduced one another with a fervour seldom summoned for their Labour opponents. “This is a government on the ropes,” the former shadow minister John Woodcock told me. It is also one that is predicted to gain seats on 5 May.

Having cast Labour as an advancing opposition, McDonnell now speaks of it as one in retreat. “[We will] hold on to as much as we possibly can,” he said on 24 April. All parties manage expectations but Labour MPs accuse McDonnell of something else: declaring failure in advance. “Like Leicester, we should be pushing for the title. Instead we sound like Villa – resigned to relegation,” the former shadow cabinet member Michael Dugher tweeted in response.

Any football manager in this position would have their future questioned, as Corbyn will if Labour sustains losses on 5 May. Unlike the seven Premier League bosses who have departed this season, however, Corbyn is almost certainly secure in his job. This is not only because Sadiq Khan is expected to become the first Labour candidate to win the London mayoralty since 2004. The party could lose 300 council seats, be beaten by Zac Goldsmith in the capital and finish third – no, fourth – in Scotland and Corbyn would still be safe.

Although it feels much longer to some Labour MPs, it is just seven months since he was elected leader by a landslide. Almost all of those who voted for him did so in the hope and expectation that he would fight the next general election. Few are likely to change their view on 5 May, however the party fares. Their loyalty to Corbyn is unconditional. Were the Labour leader challenged, he would likely win an equal or larger share of the vote than he did last year.

Yet his confirmed opponents, fewer in number than generally thought, are reserving this option. There will be no challenge before the EU referendum on 23 June, a cause that demands Labour MPs’ full energies. But an intervention after this point is still under discussion. For some, the question of whether to challenge Corbyn is less tactical than ethical. “People will ask, ‘What did you do in the war?’” one MP says.

An additional motive is the attempt of the left to consolidate its power. The Bennite Campaign for Labour Party Democracy has not just proposed amending the rules to guarantee Corbyn a place on the ballot if challenged; it has also called for the nomination threshold for leadership candidates to be reduced from 15 per cent of MPs and MEPs to 5 per cent – a move that would ensure a left presence in future contests. Corbyn’s opponents hope that the shift to the left is merely a cyclical change (with the party destined eventually to swing to the right) but it could become structural. The left aspires to succeed where New Labour failed and achieve permanent hegemony. In these circumstances, some MPs would consider what they would otherwise dismiss: a formal split.

In the view of most, Corbyn will be leader for as long as he wants. But many question how long that will be. They suggest that he could seek a midterm handover to McDonnell, his closest ally and an unsuccessful challenger in 2007 and 2010. Some Corbyn supporters privately confess that they would rather have the shadow chancellor, a more pragmatic operator, in charge. Others dismiss the belief that the Labour leader is planning an early departure from his office in the Norman Shaw South building. “He’s enjoying it,” a shadow minister told me, noting Corbyn’s improved parliamentary performances. His smile after meeting Barack Obama was that of a man basking in the Indian summer of his career.

Labour’s left is often said to be more concerned with winning power in the party than in the country. Yet a greater number of people than is usually thought believe that they will defeat the Tories at the next election. Although they may tarry, the line goes, the voters will turn to Labour. Should the party lose seats on 5 May, this faith will be tested. But it will endure.