Theresa May has told MPs it would be “an act of gross irresponsibility” for the UK to abandon its nuclear weapons.
The prime minister accused critics of the Trident system of being “the first to defend the country’s enemies”.
MPs will vote later on whether to renew the UK’s nuclear weapons programme.
Labour leader Jeremy Corbyn, who will vote against the government but whose party is split, warned of the effect that using an “indiscriminate weapon of mass destruction” could have.
But he faced repeated criticism from his own backbenchers who told him to state Labour’s official policy, which is in favour of renewal.
Labour is currently reviewing its stance on Trident, and its MPs have been given a free vote in the Commons debate.
The Trident nuclear programme, also known as the Trident nuclear deterrent, covers the development, procurement and operation of the current generation of nuclear weapons and the means to deliver them in the United Kingdom.