Neil Kinnock: If Corbyn does not change stance on Trident, Labour will lose in 2020
The former Labour leader, who lost two general elections during his time in charge, said no party can form the Government "if it sustains a stance which means unilateral nuclear disarmament".
Mr Corbyn is a long-standing opponent of nuclear weapons, and sparked anger among many Labour MPs by speaking at a CND rally in London last weekend.
Shadow Defence Secretary Emily Thornberry, who is also a unilateralist, is heading up a review of Labour's policy on Trident renewal.
But speaking to the BBC, Lord Kinnock said changing the party's pro-Trident stance would guarantee a Tory victory in 2020.
He said: "No party can win a national United Kingdom election if it sustains a stance which means unilateral nuclear disarmament."
The peer, who changed the party's previous opposition to nuclear weapons in 1989, added: "From the early 1980s really, I'd recognised the unsustainability of the unilateral nuclear disarmament policy, and I was in the very uncomfortable position of having to try to sustain it.
"I am seeking the exercise of the skills of leadership, and they do require a combination of strength and assertiveness, because parties that are ill-disciplined simply don't enjoy the confidence and support of the electorate."
Labour grandee Peter Mandelson echoed the former leader’s sentiments.
He said: "The British public have never been and are never going to be unilateral nuclear disarmers. It is just something that you could never sign them up for,” he said.