The UK's plan to increase the cap on its nuclear arsenal, criticized by peace campaigners and several governments, represents a move away from the UK's policy of non-proliferation. 

Lifting the cap from 180 warheads to 260, a 40 percent rise, was contained within the government's integrated defence review.

Questioned over the decision on BBC radio, UK Foreign Secretary Dominic Raab said: "It is the ultimate guarantee, the ultimate insurance policy against the worst threat from hostile states."

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The country had previously been reducing its nuclear weapons stockpile. In 2010, the government set a cap of 180 warheads for the mid-2020 period. 

The review is the first indication of how UK Prime Johnson envisages the country's post-Brexit military role. It noted perceived risks from nuclear-armed states, emerging nuclear states and state-sponsored nuclear terrorism, along with claims that its nuclear deterrent was needed to guarantee its security and that of its allies.

The nuclear limit expansion is just a part of Johnson's plan. The UK will increase military spending by $32 billion and deploy a new aircraft carrier, named after the country's reigning monarch Queen Elizabeth II, to Asia. There it will reinforce ongoing U.S. military manoeuvres.

A threat to international stability? 

The move comes weeks after international anti-proliferation goals were reinforced when the U.S. and Russia agreed to extend their nuclear arms control treaty. 

Russia, labeled the UK's "most acute threat" by Johnson, warned that London's decision represented a threat to "global stability."

"We find it very regretful that Britain has selected the path of increasing the number of warheads. This decision harms international stability and strategic security," said Russian presidential spokesman Dmitry Peskov.

The plan was also condemned by Iran's Foreign Minister Mohammad Javad Zarif, who was integral to the signing of the Iran nuclear deal in 2015. 

"In utter hypocrisy, @BorisJohnson is 'concerned about Iran developing a viable nuclear weapon.' On the very same day he announces his country will increase its stockpile of nukes," Zarif posted on Twitter.

"Unlike the UK and allies, Iran believes nukes and all WMDs [weapons of mass destruction] are barbaric and must be eradicated," he added.

'Dangerous new arms race'

Along with criticism from those countries criticized in the review, the move has been attacked by campaigners and former heads of state. 

The Elders, a group, founded by Nelson Mandela, of former global policymakers who campaign for peace, criticized the move.

"While the UK cites increased security threats as justification for this move, the appropriate response to these challenges should be to work multilaterally to strengthen international arms control agreements and to reduce – not increase – the number of nuclear weapons in existence," said Mary Robinson, chair of the group, and a former president of Ireland.

The executive director of the Nobel Prize-winning International Campaign to Abolish Nuclear Weapons (ICAN), said the move was a violation of international law and the UK was "pushing for a dangerous new nuclear arms race."

The review also contained announcements that would eradicate transparency on the UK's nuclear arsenal. The government will no longer give any public information on the number of nuclear warheads and missiles carried by submarines, nor will it place a public limit on the proportion of its stockpile that is operational at any one time. 

Tom Plant, director of nuclear policy at the Royal United Services Institute, wrote that these policies "will do much to negate a self-crafted diplomatic image of the UK as the most progressive of the world's nuclear-armed powers."