Russia has dismissed a warning by Defence Secretary Gavin Wiliamson that Moscow could cause “thousands and thousands and thousands” of deaths in Britain with an attack that would cripple the UK's infrastructure and energy supply.

In an interview with the Telegraph, Gavin Williamson said Russia has been researching the UK’s critical national infrastructure and how it connects to continental power supplies with a view to creating "panic" and "chaos".

Delivering his assessment of the threat from what he calls an increasingly assertive Kremlin, he said it was willing to take action “that any other nation would see as completely unacceptable”.

However, Igor Konashenkov, a spokesman for the Russian Defence Ministry, responded on Friday by saying it is likely Mr Williamson "has lost his grasp on reason".

"The minister's fear of Russia photographing electric power plants or studying the routes of British gas pipelines is like something out of a children's comic or the show 'Monty Python's Flying Circus'," Mr Konashenkov said.

"If these statements are an attempt by Wilson to attract attention to himself, he will be far from the first defence minister to try to score political points by playing up the Russian threat to the British," Mr Konashenkov added in a written response which misnamed Mr Williamson variously and throughout.

The Russian embassy tweeted a picture of the Telegraph's exclusive story, adding: "Some British politicians bear no responsibility for their words."

Mr Williamson, who is tipped as a possible future Tory leadership contender, gave his warning at the start of a new five-month-long defence review in which the Ministry of Defence is attempting to secure more money to stave off cuts to the Armed Forces.

The Chief of the General Staff this week delivered a speech warning the Army is struggling to keep up with Russian military advances.

Mr Williamson told the Telegraph that Russia was spying on Britain’s critical national infrastructure and asking "How can we hurt Britain?"

He said: “The plan for the Russians won’t be for landing craft to appear in the South Bay in Scarborough, and off Brighton Beach.

“What they are looking at doing is they are going to be thinking 'How can we just cause so much pain to Britain?'. Damage its economy, rip its infrastructure apart, actually cause thousands and thousands and thousands of deaths, but actually have an element of creating total chaos within the country.”

He said Russia was looking at the energy lines that link the UK to continental supplies and allow Britain to trade and share electricity and gas with neighbours.

Britain currently has four undersea interconnectors for electricity and three for gas, which provide energy to three million homes - a figure which will rise to eight million when further connections are built.

The Defence Secretary said: “Why would they keep photographing and looking at power stations, why are they looking at the interconnectors that bring so much electricity and so much energy into our country.

Defence Secretary Gavin Williamson credit: HANNAH MCKAY/ REUTERS

“They are looking at these things because they are saying these are the ways that we can hurt Britain.

“If we lost our interconnectors, which would be something that we know that they are looking at, there would be three million homes without electricity. In a few years time there will be eight million homes that would be dependent.

“If you could imagine the domestic and industrial chaos that this would actually cause. What they would do is cause the chaos and then step back.”

“This is the real threat that I believe the country is facing at the moment.”

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Ciaran Martin, chief executive of GCHQ’s National Cyber Security Centre, in November said recent Russian hacking activity in the UK had included attacks on the energy sector.

Mr Williamson said the Russian interest was not about “copying our infrastructure model in order to roll out east of the Urals”.

“What they are looking at doing is trying to spot vulnerabilities, because what they want to do is they want to know how to strike it, they want to know how they can kill infrastructure and by killing that infrastructure that means hurting Britain and the British people.”

He said sabotage could come from a cyber attack, from undersea activity or even a missile.

The Chief of the Defence Staff, Air Chief Marshal Sir Stuart Peach, warned before Christmas of the vulnerability of Britain’s undersea internet communications cables.

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He said if they were cut it would “potentially catastrophically affect both our economy and other ways of living”.

Lord West, a former First Sea Lord and security minister, said he was “absolutely certain Russia was looking at how to get into our critical national infrastructure” as a contingency for any future confrontation.

He said if Russia was now flagrantly prying into Britain’s infrastructure it was worrying because it appeared to suggest they no longer cared being caught.

Dr Igor Sutyagin, a Russia expert at the Royal United Services Institute, said the country’s military had decided that attacks on infrastructure were the most efficient way to cause the most damage.

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He said: “It’s not scaremongering. Technically he’s correct, but what it is necessary to keep in mind is that they are not going to attack just tomorrow.

“They are preparing, they are studying the options of how to inflict damage just to be prepared.

“They are looking for the most efficient ways to inflict the most damage if necessary, but they are not going to attack right now.”