John McDonnell has said he takes full responsibility for Labour’s disastrous election defeat, as he sought to divert blame away from Jeremy Corbyn and pave the way for Rebecca Long-Bailey to become leader.

The shadow chancellor, who ran the campaign that led to Labour losing dozens of northern English seats to the Tories, apologised and claimed that he “owns this disaster”. But he went on to blame the failure to communicate the party’s Brexit policy and media attacks on Jeremy Corbyn for the defeat as well.

Speaking on the BBC’s Andrew Marr Show, he said: “It’s on me. It’s on me. Let’s take it on the chin. I own this disaster. I apologise to all those wonderful Labour MPs who’ve lost their seats who’ve worked so hard … If anyone’s to blame it is me. Full stop.”

Corbyn has not apologised for the election defeat although he has said he is “very sad” about the result. He released a video on Sunday with the comment “our time will come”, in an apparent attempt to defend his policies and cement his legacy.

“Make no mistake, Labour is the greatest force for progressive change this country has ever known. And though this wasn’t our moment, our time will come,” he said. “Over the last four years we have built a new movement which isn’t going away. For those that feel disheartened and feel like giving up, I say stay and fight for a better society.

“And to those that haven’t joined us, join the Labour party today. Be part of the resistance to Boris Johnson and the politics of fear. This starts now. Campaigning to protect our communities, our national health service and public services must be relentless. So that when elections come, we will be bigger and stronger. We will win.”

Corbyn made no reference to his intention to step down but McDonnell confirmed they would both leave their posts within the next eight to 10 weeks and he suggested his favoured candidate for the leadership would be Rebecca Long-Bailey, a longtime ally.

He said he would like to see a woman take over, and preferably someone from outside London, listing Angela Rayner and Dawn Butler among other possibilities.

Lisa Nandy, a Labour backbencher and former shadow cabinet minister under Ed Miliband, said she was “seriously thinking” about running.

Nandy told Marr that there was a “very, very hard road” to regain the trust of Labour voters in towns across the north of England.

“I think it’s right to say that we need to be much more rooted in those parts of the country. I think that goes beyond the leader though,” she said.

“There’s absolutely no reason why decision-making is concentrated in central London. Our Labour headquarters, in my view, should move out of London, our regional offices should be empowered to take real decisions, we should move our party conferences back to towns as well as cities.”

Jess Phillips, the outspoken backbencher and women’s rights campaigner, could also run, plus Yvette Cooper, a former Labour minister who was a losing candidate against Corbyn in 2015. Other leading contenders include Keir Starmer, the shadow Brexit secretary, and Emily Thornberry, the shadow foreign secretary.

However, there is a backlash within some quarters of the party against Starmer and Thornberry, who were instrumental in pushing Labour towards a position in favour of a second referendum.

Caroline Flint, a former Labour minister who lost her Don Valley seat, said the only two candidates worth considering were Long-Bailey and Nandy, as they were not complicit in pushing the party towards a more remain position.

She claimed on Sky’s Sophy Ridge on Sunday that Thornberry had told a Labour colleague in a leave-voting seat: “I’m glad my constituents aren’t as stupid as yours.”

Flint said the next leader should not be “Corbyn without a beard”.

Thornberry, who has not yet confirmed whether she is running, hit back saying: “This is a total and utter lie. I have never said this to anyone, nor anything like it, and I hope, needless to say, it is not something I would ever think.”

Richard Burgon, the shadow justice secretary and an ally of Corbyn, had been considered a possible contender but he threw his weight behind Long-Bailey and suggested he could run as her deputy.

Speaking on Sky, he blamed the party’s Brexit position of promising a second referendum without saying how it would campaign, as well as a “character assassination” of Corbyn by rightwing media.

“I think it was right to attempt to bring the country together on that basis. Did it fail? We’ve got to be open, it did fail,” he said. “It was a disastrous election result and for that we are truly sorry … I think the biggest mistake the Labour party made was perhaps underestimating the desire for people who had voted leave to leave the European Union.”