Jeremy Corbyn warned Labour must gain 'hundreds of seats' in council elections
A study of council election results from the last 42 years shows that opposition parties in non-general election years nearly always make huge gains against their government opponents.
Opposition party leaders also historically do well in their first local elections in charge - the situation Mr Corbyn will be in come May.
The Labour local government analysis of results dating back to 1974, leaked to this website, shows that the average council election gains for an opposition party in a non-general election year is 434 seats.
The last time a party in that situation lost seats was Labour in 1985, when it was tearing itself apart over Militant. Even then, the party still lost fewer council seats than the Tories.
Labour also lost seats in 1982 under Michael Foot, but that came during the Falklands War and after a party split led to the formation of the rival SDP/Liberal Alliance.
Average gains for new opposition party leaders is 515 seats, while parties heading for a general election victory gain, on average, 526 seats.
Even at the height of New Labour’s popularity in 1998, the William Hague-led Tories still gained 256 seats while Labour lost 88.
And in 1981, Michael Foot’s first local elections as leader saw Labour make 988 gains.
Aides close to Jeremy Corbyn have insisted that because Labour did well at the 2012 council elections, gaining 823 seats, the party could well go backwards in May.
But a senior Labour source said: “We’ve given up our historic mission. Clause One of the Labour constitution makes clear that our aim is to ‘organise and maintain in Parliament and in the country a political Labour party’.
“But we are now a party that is happy to lose council seats in a non-election year.
“If that happens, it would be the single worst performance by an opposition party in local government history.”
The source added: "Only when we split and the country is at war did we lose anything like 200 seats in opposition.
"In the context of all past local elections, Labour have to gain in 2016."
Michael Dugher, who Jeremy Corbyn sacked as Culture Secretary in January, said: “The May elections are a huge test for Labour and for Jeremy Corbyn. He has to show that under his leadership we are making real progress in terms of getting back in touch with the public and gaining real support.
“We cannot afford to become a Labour party that the Tories no longer fear. We mustn’t allow the Tories to get away with doing whatever they want because Labour simply isn’t at the races.
“Jeremy must demonstrate in May that we can make real gains in every corner of the country – not just London.”
Liz Kendall, who Mr Corbyn beat to the Labour leadership last September, said: "I think we're going to win the mayoralty in London, and Scotland doesn't look good.
"But the real test is what happens in the English local elections. Even Michael Howard won the 2004 local elections by 12 points, but he then lost the general election the next year.
"The fact that this is the first council elections under a new leader will tell us a lot about the party and its chances."
PoliticsHome revealed yesterday that Labour's slogan for the local elections will be 'Standing Up, Not Standing By'.
Shadow Communities Secretary Jon Trickett set out the party's election strategy at a meeting of MPs on Monday evening.
One backbencher present said: "Jon's presentation was symbolic of the situation we're in - it was an embarrassing shambles. During it, one MP said audibly 'is this the Monty Python show'?"
A shadow minister said: "Jeremy and Trickett took half an hour to talk about our election strategy. How can it take so long to say: we're screwed?"
A Labour source said: "We are campaigning hard for every vote in this important election, to stand up for working people who have been let down by the Tories.
"Coming so soon after what was a disappointing result in 2015, Labour is rebuilding with a focus on the 2020 general election. The 2016 local elections are an early step on that road."