Labour leader Jeremy Corbyn can win 2020 election, but will wreck national security says Michael Gove

Michael Gove has surprisingly claimed that that new Labour leader Jeremy Corbyn could win the next general election in 2020. But the top Tory warned that the left-winger would undermine the national and economic security of the UK if he entered Number 10.

The justice secretary insisted that his party is not "gleeful" after the Islington North MP secured almost 60% of the vote in Labour's leadership election to appoint the successor to Ed Miliband on 12 September. Gove said that the Conservatives' attitude is instead "sombre and respectful" of Corbyn's mandate.

"To win an election by the margin that he has means that any of us who are democrats have to congratulate him on that. The attitude of most of us who are Conservatives is sombre, respectful of Jeremy Corbyn's mandate, but also concerned about what it means for the country," he said on BBC's Andrew Marr show. "We have to face up to the fact that Jeremy Corbyn is the person Labour want to have as prime minister now and if he were prime minister that would be a real danger to our national security but also to the economic security [of the UK]."

The comments give an early indication that the Conservatives plan to attack Labour over Corbyn's anti-nuclear credentials and the left-winger's anti-austerity politics. Michael Fallon, the defence secretary, said just after Corbyn's victory that the Islington North MP could even be a "serious risk" to the security of families across Britain.

"Whether it's weakening our defences, raising taxes on jobs and earnings, racking up more debt and welfare or driving up the cost of living by printing money – Jeremy Corbyn's Labour Party will hurt working people," Fallon claimed. "This is a very serious moment for our country – the Conservatives will continue to deliver stability, security and opportunity for working people."

Tom Watson, Labour's new deputy leader who stepped in for Corbyn on the Marr show, admitted he did not "precisely" know what Corbyn's defence policies were, but the West Bromwich East said he would lobby the leader over the issues.

"Nobody wants to live in a nuclear world, but it is how you disarm. I think the deterrent has kept the peace in the world for the last century", Watson said.

He added: "I think Nato has kept the peace in the world for half a century. I aim to convince him of the merits of Nato, it has kept the peace in Western Europe and it was created by one of Labour's greatest ever foreign secretaries, Earnest Bevin. I hope we can have that debate in the party."