Boris Johnson has announced plans to lift a cap on the UK's nuclear weapon stockpile as he set out his foreign policy strategy in a major defence review.
The UK is one of nine countries in the world to have nuclear weapons although its arsenal is dwarfed by those of Russia and the United States.
In response to the "evolving security environment", the prime minster has announced that the government will lift the limit on the number of nuclear warheads that was previously put in place as part of a global effort for disarmament.
The UK had committed to building no more than 180 warheads by the mid-2020s, but now this number could increase to 260.
Lifting the cap came as Johnson set out his geopolitical strategies for the coming years in the Integrated Review Of Security, Defence, Development And Foreign Policy paper, which was published on Tuesday.
The review said a policy of "deliberate ambiguity" will mean the public will not be given figures for the operational stockpile or how many missiles and warheads are deployed.
The announcement has already been met with severe criticism and concern.
Among the critics was Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons, who branded the plan “very dangerous”.
She told BBC Radio 4’s World At One: “I think it is an outrageous decision. It is irresponsible and actually very dangerous.
“Not only does it go against international law, a law that Britain has signed to pursue nuclear disarmament, but it really makes the world more insecure.
“This worsening of the international security situation that the government is talking about, the government is making that happen now, they are actually contributing to a much more insecure and unstable world.”
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Fihn said it amounted to a 40% increase – a scale not undertaken by any nation since “the height of the Cold War”.
Which countries have nuclear weapons?
The nine countries who currently have nuclear weapons – some legally and some illegally – with an estimated 13,400 warheads between them, according to the Federation of American Scientists (FAS).
Five nations are officially recognised as possessing nuclear arms by the Nuclear Nonproliferation Treaty (NPT).
These are the UK, China, France, the United States and Russia.
But there are also four nations who hold the weapons illegally – India, Pakistan, Israel and North Korea.
Russia has the most nuclear weapons followed by the US.
While the official number of nuclear weapons tend to be a state secret, the FAS estimates that Russia has 6,372.
Number of nuclear weapons per country
This is closely followed by the US, which has an estimated 5,800.
In fact, the FAS says that approximately 91% of all nuclear warheads are owned by Russia and the US.
Meanwhile, no other nuclear-armed state sees a need for more than a few hundred nuclear weapons for national security.
That's why China, which comes in third, has just 320 in comparisons to the thousands owned by Russia and the US.
France follows with an estimated 250 warheads, then the UK with an estimated 195.
How the number of nuclear weapons are distributed around the world
Out of the countries that hold nuclear weapons illegally, Pakistan has around 160, India has around 150, Israel has around 90 and North Korea comes in last with around 35.
But these totals also include weapons that are still intact but are queued for dismantlement.
As countries commit to nuclear disarmament, the number of weapons that remain in their military stockpiles are decreasing.
These stockpile numbers can also be broken down into different categories depending on whether the weapons are deployed on launchers at military bases or are being kept in reserve.
According to the FAS, the entire "military stockpile" includes all active and inactive warheads that are in the custody of the military and earmarked for use by commissioned deliver vehicles.
Meanwhile, "deployed strategic warheads" are those deployed on intercontinental missiles and at heavy bomber bases.
Only Russia, the US, France and the UK have deployed strategic weapons, coming to a total of 3,720 globally.
"Deployed nonstrategic warheads" are those deployed on bases with operational short-range delivery systems.
These are less common with only the US holds these nonstrategic weapons with 150 in its arsenal.
Most warheads in the world are in reserve or "non-deployed", meaning they are in storage rather than deployed at military bases.
An estimated 9,320 nuclear warheads are in storage around the world with all nine countries keeping weapons in reserve.
For Israel, Pakistan, India and North Korea, their entire military stockpiles are non-deployed, according to the FAS – meaning none are currently deployed.
Only two nuclear weapons have ever been used in warfare since they were first developed by the US during the Second World War.
The US dropped two bombs on the cities of Hiroshima and Nagasaki in 1945, killing almost 200,000 people in total.
Both Russia and the US continued to build up their stockpile of nuclear weapons during the Cold War as tensions escalated.
The latest nation to build nuclear weapons is North Korea, which carried out its first nuclear test in 2006.
The FAS estimates there have been over 2,000 nuclear tests conducted to date.
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