Jeremy Corbyn insists he will be on ballot paper to take on Angela Eagle and remain Labour leader

Under-fire Labour leader Jeremy Corbyn has come out fighting ahead of a probably bruising contest to decide the future – and perhaps fate – of the Labour Party, insisting he will be on the ballot paper and calling on Labour followers to unite and fight Tory austerity. In his first TV interview for weeks, Corbyn told the BBC's Andrew Marr that he had consulted lawyers who confirmed he did not require the support of 51 MPs, raising the prospect of legal action of he is barred from standing by a ruling from Labour's National Executive Committee (NEC).

Asked by Marr how he could lead an effective opposition with four-fifths of the Parliamentary Labour Party against him, Corbyn said: "We're only ever in Parliament because of the work of Labour Party members, supporters and, of course, Labour voters and I urge then to recognise that, but also I'm keen to reach out."

Corbyn also insisted reports he had thought of stepping aside were untrue and that people should not believe everything they read in newspapers. "There's no wobbles, there's no stress, there's no depression," said Corbyn. Real stress, he said, came from not knowing how to feed your kids or how to pay the rent.

Shadow business secretary Angela Eagle is set to launch her leadership bid on Monday, 11 July. It is still unclear if Corbyn will automatically appear on the ballot paper as the incumbent candidate. Labour's NEC will make a ruling soon, but Len McCluskey, leader of the Unite trade union, has warned of the party facing consequences if the left-wing MP is blocked from standing.

"I must warn that any attempts to keep Jeremy Corbyn, elected just 10 months ago with an enormous mandate, off the ballot paper by legal means risks a lasting division in the party," said McCluskey. "It is time for everyone to commit to a democratic and dignified procedure as the only way to avert such a disaster for working people."

Both of the UK's main political parties – the Conservatives and Labour – are facing a crisis over their leadership and future. A number of senior Conservative MPs have threatened to quit the party if Angela Leadsom is elected leader, which would make her the UK's second female prime minister.

Leadsom sparked an outcry when she told The Times that being a parent gave her an edge over favourite Theresa May. The previous week May, the current home secretary, had told The Sun that she and her husband were unable to have children.