Labour would have won the 2017 general election had its MPs not launched a leadership challenge in 2016, Jeremy Corbyn has suggested in his first interview since the election of Keir Starmer.

In a wide-ranging interview with the Benn Society, a new political education initiative led by trade unionist and London Assembly candidate Liam Young, Corbyn said divisions within the party in the wake of the EU referendum had denied it an outright victory in Theresa May’s snap election.

“We went into the general election in 2017 when they’d all written us off, and were astonished at how close we got to winning,” Corbyn said. “We were within a whisker of winning that general election.”

He went on to suggest that events the previous year, when the vast majority of his shadow cabinet resigned, 172 MPs passed a motion of no confidence in his leadership and Owen Smith launched an ill-fated leadership bid, had been a block on electoral success for Labour.

“And had the party been more united than we had been in 2016, I'm absolutely confident we could have won that general election, because it was all absolutely going our way and our manifesto was very much in tune with the way people were feeling."

Corbyn also signalled his support for mandatory reselection of Labour MPs and spoke of the need for his supporters on the left to frame their arguments around policies, rather than personality, as they come to terms with a new political reality in the wake of his replacement as leader by Starmer.

With some on the left leaving the party – or threatening to do so – in the wake of Corbyn’s departure, the Benn Society, which also secured John McDonnell’s first major interview since quitting as shadow chancellor on 4 April, aims to convince Corbyn's supporters to stay and fight within the party as its namesake did. Some on the Labour left are concerned that activists who joined to support Corbyn's leadership see his politics as a temporary aberration in the party's history, rather than a permanent fixture of its internal debate.

“The idea behind the Benn Society is a simple one: we want to show that the left is not a new force within the Labour Party, but a constant one,” Young, a Communications Workers Union staffer, told the New Statesman. “Tony Benn’s political philosophy centred around achieving change through the vehicle of the Labour Party and we’ve created this educational tool to demonstrate the historical context of the left within the party. Some have celebrated Jeremy’s departure as leader but they have done so prematurely. My generation has been inspired by his politics and we will keep the flame alive.”

Asked where the Labour left should go next, Corbyn told Young: “Don’t go into personal abuse and personal attacks. Don’t go into looking for sectarian arguments. Instead, look for issues that can unite and mobilise the left… Frame the arguments and debates within the party around policies and principles, and not around individuals. Because if we spend all our time attacking each other because of our like or dislike of each other individually, it doesn’t actually get us anywhere in the end.”

Corbyn suggested the Labour left should instead focus its energies on responding to the economic and public health challenges posed by coronavirus, workers’ rights, global inequality and a human rights-based foreign policy.

Reflecting on his four and a half years as Labour leader, he went on to speak of the difficulty he had faced in reforming the party’s internal structures – particularly on reselection processes for MPs, historically a cause celebre for the Bennite left.

"It was extremely difficult to reform the party,” Corbyn said. “We did make some changes, which changed the basis on which candidates for leader and deputy have to be nominated by constituency parties and affiliated organisations, as well as just MPs. The balance has moved slightly away from the exclusivity of the parliamentary Labour Party.

“The threshold for holding trigger ballots has been changed, so it is therefore not as difficult as it was for a trigger ballot to be held. There were debates over whether we should have a mandatory reselection process or not. That did not find enough support, particularly amongst unions, at the party conference [in 2018], so we have the system we now have.

He indicated that he remained supportive of mandatory reselection. “My own view is that democracy is best served when all members are fully involved in selection processes, and that MPs themselves are accountable to that process. In truth, most MPs have very little to fear from that process indeed... I think the points that Richard Burgon made during his deputy leadership campaign about bringing back mandatory reselection were actually well made and well taken, and I think it is an issue that will come up again."

Unlike his immediate predecessors as Labour leader did after stepping down, Corbyn also stressed that he would continue to assert himself from the backbenches. “I hope those policies will continue, and, indeed, during the leadership debates, the three leadership candidates all essentially confirmed that the anti-austerity political agenda should continue... I hope that is the case, and I hope that they recognise that an accommodation with the Tories is not acceptable, and that has to be a point of unity of our party. I will certainly be making that case very strongly, as John and others have: the need to maintain a socialist economic policy.

"I won't be going on world tours sponsored by any big business organisations, I have no directorships and don't intend to have any – I'm not interested in that sort of life or activity at all. My job will be being MP for Islington North. It will be a lot of writing about the experience of the past five years and ideas for the future, and it will also be a lot of campaigning work and supporting different organisations and campaigns. I've offered to help also with political education in the party and in unions before. Because surely the experience of life ought to be something one passes on for future generations to at least understand what went on? My political activity is not going to diminish in the slightest: I'll be as busy as I've always been.”