Jeremy Corbyn has suggested the UK could have Trident submarines without nuclear weapons, a move that would mean disarmament while protecting defence jobs in Scotland and Cumbria.

The Labour leader raised the idea on the BBC’s Andrew Marr Show as a possible compromise between his opposition to nuclear weapons and the position of the trade unions, which want to protect the jobs of workers who will build replacement Trident submarines.

The shadow defence secretary, Emily Thornberry, later confirmed that the idea would be considered as part of the defence review, launched on Friday. Thornberry said it was the “Japanese option” to maintain submarines and nuclear capabilities without actually having operational nuclear weapons.

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Corbyn, who opposes nuclear weapons, has said he wishes to accommodate those who want to keep Trident submarines, including the unions representing defence workers, and more than half of his shadow cabinet.

In an interview over the weekend, the Labour leader argued it was not a binary decision on whether to replace Trident submarines, suggesting a possible compromise. Pressed on the Marr Show as to what this meant for Trident, Corbyn said: “They don’t have to have nuclear warheads on them.”

Asked again whether he was suggesting that new submarines could be built to be used without nuclear warheads, Corbyn said: “There are options there. The paper that Emily Thornberry has put forward is very interesting and deserves study of it. I hope there will be a serious and mature response.” He also stressed that he would want to maintain employment for people in the defence industry, who would be involved in building Trident submarines, as a “first priority”.

Thornberry told the BBC’s Sunday Politics: “The way that it works is that the Japanese have got a capability to build a nuclear bomb...[but] you can then put them on to, or you can use them, in various delivery forms. So that’s a possibility, that is an option.” She said she would not speculate on what the review would recommend but she added that Corbyn “said there’s a number of options, and I said the Japanese already have this as the way that they use theirs”.

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Labour MPs must decide if they support or oppose Trident before a parliamentary vote in the spring on whether the nuclear submarines should be replaced. Given that Corbyn cannot officially change party policy to oppose Trident before Labour’s conference in the autumn, it is looking increasingly likely that he will offer his party a free vote.

Len McCluskey, the general secretary of the Unite union, told Sky’s Murnaghan programme that it would be sensible for Corbyn to let MPs vote freely. He also suggested that he could be open to the idea of submarines with no nuclear weapons on them. “There’s all kind of different options that will be debated and discussed,” McCluskey said.

He said the decision on proceeding with building the nuclear submarines would be passed in parliament but defence diversification would be discussed after that as part of Labour’s review.

Thornberry, who replaced the pro-Trident Maria Eagle as shadow defence secretary in a reshuffle earlier this month, said her review would be serious and and ask far-reaching questions. Asked what she thought about the idea of replacing Trident submarines without nuclear warheads, she told Murnaghan: “The first thing I would say is calm down.

“The defence review was launched on Friday. We need to start with what are the current threats. Our overwhelming priority is to make sure Britain is safe. We need to make sure we have policies that address 21st-century threats, not 20th-century threats.”

Thornberry also said there was a “debate to be had about how many jobs are specifically related to the renewal of Trident”. She avoided the question about why Ken Livingstone, the former mayor of London, has been sidelined from her defence review but made clear she was now in charge.