The Labour leader Jeremy Corbyn has questioned the effectiveness of Trident, as MPs prepare to vote on renewal of Britain's nuclear deterrent.
Speaking in the Commons, he said: "What is the threat that we are facing that over a million people's deaths actually deters?
"It's not from the so-called Islamic State - their poisonous death cult glories in killing as many people as possible, as we've seen brutally in Syria, to east Africa, from France to Turkey.
"It hasn't deterred our ally, Saudi Arabia, from committing dreadful acts in the Yemen. It didn't stop Saddam Hussein's atrocities in the 1980s or the invasion of Kuwait in 1990. It didn't deter the war crimes in the Balkans in the 1990s, nor the genocide in Rwanda.
"I do not believe the threat of mass murder is a legitimate to go about dealing with international relations."
Another Scottish independence referendum is fast approaching, SNP warns, after Westminster voted to renew Trident.
Labour MPs reacted angrily after Jeremy Corbyn referred to the party's policy on the UK's nuclear deterrent in the past tense.
Nicola Sturgeon has accused the UK Government of "playing games" over Trident, ahead of MPs voting on the renewal of the nuclear deterrent.