Jeremy Corbyn says he doesn't think David Cameron would use nuclear weapons
Marr asked Corbyn about his opposition to Britain's fleet of Trident submarines, which carry the country's nuclear missiles. Corbyn is an outspoken critic of nuclear weapons, and has made it clear that he supports efforts to eliminate nuclear weapons.
Corbyn has said in the past that he would not choose to use nuclear weapons if he were Prime Minister. That's seen by some people as making Britain's nuclear weapons useless - they're intended to act as a deterrent, but that won't work if the Prime Minister has publicly said he won't use them.
During the interview with Andrew Marr, Corbyn reaffirmed his opposition to nuclear weapons. "If anybody uses a nuclear weapon ... it is catastrophic to the whole world," Corbyn said. "I don't think David Cameron would use it either."
However, in the past David Cameron has said that he would use nuclear weapons. Cameron appeared on the Andrew Marr show last year and said that "you have to accept there are circumstances in which [the use of nuclear weapons] would be justified. If you give any other answer then you are, frankly, undermining our national security, undermining our deterrent."