BORIS Johnson’s plans to increase the UK’s stockpile of nuclear weapons will contribute to the “growing competition and distrust between nuclear-armed states”, a respected US think tank has said.

The Washington-based Arms Control Association (ACA) said the move to increase the UK stockpile by more than 40% and reduce transparency was a “needless and alarming reversal” of the longstanding policy to reduce the number and role of such weapons.

Johnson announced the new strategy for Britain’s post-Brexit role in the world, with China on the rise, saying the military would have to be “match-fit for the modern world”.

However, it has been fiercely ­criticised, particularly in Scotland, where the Trident nuclear warheads are stored on the Clyde.

The ACA said the move was inconsistent with the British Government’s prior pledges under the 1968 Nuclear Non-Proliferation Treaty (NPT).

“The review attributes the need to increase the total stockpile ­ceiling from 180 warheads to 260 warheads to ‘the evolving security environment, including the developing range of technological and doctrinal threats’, but it does not explain how raising the number of warheads will enhance deterrence against these threats,” it said.

Daryl Kimball, ACA’s executive ­director, told The National there was no compelling military or strategic ­rationale to justify the increase.

“The UK’s decision to increase its arsenal comes without any clear explanation about who or what these additional warheads are intended to deter, and it breaks with earlier commitments by the UK ... that it would cap its warhead stockpile to 180,” said Kimball. “Just one nuclear-armed submarine, carrying as many as 128 thermonuclear warheads, each with an explosive yield of 100 kilotons or greater, could devastate a large country and kill tens of millions of people.” He said that like the US, the UK’s past commitment to transparency about its nuclear forces “has set it apart” from other nuclear powers: “Both governments have rightly criticised China for its excessive nuclear secrecy, for example. Such opacity is irresponsible and undemocratic.”

The summer NPT review conference was already poised to be difficult, given the Trump administration’s efforts to expand the US nuclear arsenal, Russia’s development of new nuclear delivery systems and China’s modernisation and expansion of its nuclear forces.

“The UK’s decision to increase its arsenal and clamp down on transparency will further worsen the ­atmosphere,” said Kimball.

“Under the NPT, the UK is obliged to reduce the role and number of nuclear weapons and to engage in good faith negotiations on disarmament. It is, sadly, doing neither, and its actions today increase rather than reduce the risk of more dangerous global nuclear arms racing in the years ahead.

“It is also galling to see the Johnson Government so completely out of step with the Biden administration, which has pledged to ‘take steps to reduce the role of nuclear weapons in our ­national security strategy’.”

“The bottom line is the UK ­under PM Johnson and FM [Foreign ­Minister] Raab are going in the wrong direction by increasing its emphasis on and number of deployed nuclear weapons without any clear military or strategic justification.”