The UK has a “clearer appreciation” of its status as a nuclear-armed power “than perhaps we have had for some time” amid Russia’s war against Ukraine, a top official has signalled.

David Williams, the most senior civil servant at the Ministry of Defence (MoD), said there was currently no plan for Britain to increase further the number of nuclear warheads it holds, but revealed it was something that is being kept under review.

He also voiced concern about a nuclear-armed Russia under President Vladimir Putin, whose conventional forces appear to be performing badly on the ground in Ukraine.

“An unpredictable and disappointed Putin feels to me a dangerous one,” Mr Williams said.

“That calibration of the threat is something we absolutely need to be alive to.”

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Mr Putin has raised the spectre of nuclear war with NATO allies and put his nuclear-armed forces on high alert since the start of his invasion of Ukraine.

But Mr Williams said Moscow’s “nuclear posturing” – while “clearly worrying” – is just rhetoric and is failing to deter NATO allies from bolstering defences across the alliance’s eastern flank and supporting the Ukrainian military.

The senior mandarin was speaking alongside Admiral Sir Tony Radakin, chief of the defence staff, at an event at the Institute for Government think-tank in London on Thursday.

Both men gave short remarks, including about plans for the future of the UK armed forces and on the crisis in Ukraine, before taking questions.

Reflecting on a year after the UK published a sweeping review of its defence and security policy, the MoD’s permanent secretary gave strong support to Britain’s nuclear deterrence – which comprises a fleet of four nuclear-armed submarines.

One boat is permanently at sea, ready to fire if needed.

Mr Williams said the “re-emergence of state-based competition underlines for me the importance of the UK’s nuclear deterrence”.

He said: “I think we have a clearer appreciation of our role as a nuclear weapons state than perhaps we have had for some time.”

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The Integrated Review, published in March 2021, reversed a planned reduction in Britain’s nuclear warheads, saying a new cap would lift to 260 from 180.

Asked whether the UK might need to look again at a possible further rise in the number of warheads, Mr Williams said: “I don’t think we have any immediate plans to increase the stockpile… It is something we will keep under review.”

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