A no-deal Brexit could lead to a general election in 2019, with a “real chance” that Jeremy Corbyn could be voted in as prime minister, the leader of the UK’s largest trade union said.

Len McCluskey, the general secretary of Unite The Union, said if Theresa May fails to strike a deal on Britain’s European Union departure by this time next year, her Government could collapse.

But he said the Tories would try to cling on in No 10, aided by the establishment, who he claimed are “scared stiff” of Mr Corbyn becoming prime minister.

The union chief said: “If there’s no deal I believe the Government will fall and we will have a general election. And I think there would be a real chance of Labour winning that election and Corbyn coming to power.”

He said he had never believed claims in the immediate aftermath of June’s snap election – in which Ms May lost her parliamentary majority and had to do a deal with Northern Ireland’s Democratic Unionist Party (DUP) – that there could be another ballot this year.

Mr McCluskey, speaking at Unite’s Scottish policy conference in Aviemore, said: “The Tories exist for one reason only and that is to have power. I knew she wouldn’t give up power and the Tories wouldn’t give up power.

“My prediction, more a hope, is that we have a general election in 2019.

“I believe that the issue of Brexit and the likelihood at the moment of no deal – and the powers that be will do everything to come up with a deal because what does look to be a certainty is if they come back with a no deal then Parliament will reject it.

“The DUP couldn’t support it, because of the issue of the hard border in Ireland, there’s a number of Tories who couldn’t support it and Labour and the SNP would reject it and Theresa May would fall.

“Then I think we would be into an election in 2019.”

He added: “This deal has got to be produced by October of next year, this time next year there has to be a deal. It’s not March 2019 because they need a deal next year so the other 27 nations can go through their process of agreeing it by March 2019.”

But he said the political elite would “move heaven and earth” to prevent the UK from exiting Europe without a deal.

Mr McCluskey said: “One thing that they are scared stiff of at the moment is a Corbyn Labour government. If this was Tony Blair or Gordon Brown or Ed Miliband, they would be more relaxed.

“With Corbyn they are scared stiff that a Labour government under his leadership will actually change the power axis within our nation.”

He told union activists “that’s how close we are, that is what is within our grasp” and added: “We now have an opportunity to transform our society, so I’m hoping for 2019 and I do believe Brexit is the issue that could bring this Government down.”