The UK’s former ambassador to Russia has criticised senior ministers for “shooting their mouths off”, singling out Defence Secretary Gavin Williamson for displaying a lack of seriousness amid the deepest crisis in relations with Moscow since the end of the Cold War.

Speaking exclusively to The Independent, Sir Rodric Braithwaite, took aim at the Cabinet minister following comments in which he told Russia to “go away and shut up“, sparking retaliatory insults from the Russian Foreign Minister and others in Moscow.

Sir Rodric, who was the UK’s man in Moscow during critical years of the Cold War, also attacked other senior ministers whom he said “have come out much too early, saying things that are much too wild”, as the UK seeks to build pressure on Vladimir Putin over Salisbury nerve agent attack.

It follows a Commons appearance from Foreign Secretary Boris Johnson early on in the crisis in which he sparked news stories that England may pull out of the football World Cup in response to the attack, something which later had to be clarified.

The former high-ranking diplomat’s comments echo those of Home Secretary Amber Rudd, who last week insisted on keeping “cool heads” following Mr Johnson’s intervention, meanwhile he goes on to praise Theresa May’s performance as “judicious”.

Sir Rodric, who served between 1988 and 1992, spoke as events quickly developed in the ongoing saga following the attack in Salisbury that involved a Russian-made “military grade” nerve-agent.

With former Russian spy Sergei Skripal, his daughter Yulia and a British police officer still in hospital, Ms May used a speech at a party forum to say the UK would not tolerate any threat to life on British soil.

Theresa May warns Russia UK will 'never tolerate threat on life of British citizens'

On Saturday Mr Putin also announced the expulsion of 23 UK diplomats in retaliation to expulsions announced by Ms May earlier in the week.

Praising the Prime Minister approach so far, Sir Rodric said: “She’s been rather judicious; she hasn’t rushed the process.

“I think in a very difficult set of circumstances, in the highly charged atmosphere, a lot of people are shooting their mouths off, I think she’s performed rather well.”

It follows the Prime Minister’s decision to blame the attack on the Russian state, expel its diplomats and execute asset freezes after Moscow failed to respond to the Government’s 24-hour deadline for an explanation of how the Novichok nerve agent came to be used on British soil.

Asked about the Defence Secretary’s comments on Thursday, Sir Rodric continued: “I think I hinted at what people like him and some of his wilder colleagues have been saying. It lacks seriousness.

“Whether you like Russia or not, it is a big country, which now has rather a lot of influence in the world – whether you like it or not. To tell it to go away and shut up is not very serious, in my view.”

Russian Foreign Minister responds to Gavin Williamson: Russia has 'stopped paying attention'

He added: “I wouldn’t be ruder than that, but it seems to me that he and some of his senior colleagues have come out much too early, saying things that are much too wild, in contrast to Theresa May.”.

Asked whether the Prime Minister should confront Mr Williamson over his incendiary remarks, Sir Rodric, also a foreign policy adviser to former Prime Minister John Major, said: “Well, she has a difficult domestic political situation to mange, to put it mildly.

“She has to make her own judgements about who she tells to shut up.”

On Jeremy Corbyn’s refusal to blame Russia on Wednesday in the House of Commons, Sir Rodric said: “This is not a situation in which absolute certainty and absolute proof, particularly of who gave the order, is ever going to be available. So one has to make a judgement.”

Sir Rodric Braithwaite was the highest ranking diplomat in Russia between 1988 and 1992 (Youtube)

He continued: “There is a limit beyond which it doesn’t make sense to say we’ve got to wait until we get more proof.

“I think it was a misjudgement on Corbyn’s part to combine his remarks about the events in Salisbury, with other remarks about the Tories receiving donations from Russian oligarchs and about money laundering in the City.

“Both of those are perfectly legitimate comments – personally I think they are both things that should be investigated further. But that wasn’t the moment to say it. I think that was a political misjudgement, which is being exploited by his political enemies.”

He later added: “If there is a secret information about who gave the order, available to British agencies, they are almost certainly not going to reveal it because they won’t want to compromise their sources. I think it’s quite difficult to imagine how they would get such information, but maybe they have done. And we won’t know.”

Russian Foreign Minister responds to Gavin Williamson: Russia has 'stopped paying attention'

While Sir Rodric described the current diplomatic crisis between the UK and Russia as a “highly emotional confrontation”, he urged caution about referring to the current situation as a “new Cold War”.

“It was a binary confrontation between two super powers and their respective allies. It was a nuclear confrontation, which if there had been a nuclear exchange would have killed hundreds and hundreds of millions of people, and it was a hair-trigger confrontation.

“The order to launch could have been given within 15 minutes of the warning.”

He added: “It’s a paradox – it was a much simpler situation, it was a much stabler situation because each side was terrified of the other and neither of them ever wanted to trigger a nuclear war, or get anywhere near it.

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“But of course these great machines of rockets and submarines and things are all subject to technical error ,and of course human being are also subject to blowing a gasket. So it was a pretty frightening situation – and that is not where we are now.”

At a speech in London, the Prime Minister said Moscow was in “flagrant breach” of international law over the Salisbury incident, a position since backed by the US, France, Germany and others.

She said: “Many Russians have made this country their home. And those who abide by our laws and make a contribution to our society will always be welcome.

“But we will never tolerate a threat to the life of British citizens and others on British soil from the Russian Government.”

A Russian response to the British measures had been expected for several days and when it came, it went further than expected.

Apart from the expected tit-for-tat expulsions, the Ministry of Foreign Affairs announced it is stopping all British Council activities “due to legal irregularities” and revoking its agreement for Britain to operate a consulate-general in St Petersburg.