Boris Johnson’s criticism of Jeremy Corbyn over Labour’s response to the Salisbury nerve agent attack is “not at all helpful”, one of the foreign secretary’s own junior ministers has said.

Mark Field, a Foreign Office minister, criticised Mr Johnson for calling the Labour leader Moscow’s “useful idiot” and suggesting he had given Moscow “false credibility” by refusing to blame Vladimir Putin’s regime unequivocally for the poisoning of Sergei and Yulia Skripal.

The foreign secretary used an article in The Sunday Times to renew his attack on Mr Corbyn, who he said was playing “Putin’s game” and “shames himself” by giving credence to Russia‘s claims.

Mr Field told the BBC radio 4’s Westminster Hour: “We all know Boris has a style and there’s also a style that the rules of ordinary political gravity don’t apply to Boris Johnson – he gets away with his style.”

Responding to the comments about Mr Corbyn, he said: “I would always try and play the ball and not the man when it comes to these things. I think to get personal about it is not helpful at all.”

In his article, Mr Johnson wrote of Mr Corbyn: “Even now he cannot bring himself unequivocally to say that the Russian state was responsible. Every time he allows himself to speak freely he reverts to his comfort zone, his infantile leftist background of sympathy for any country, any movement, however unappealing, that is hostile to Britain.”

“I will not mince words: this is cynical nonsense and Corbyn shames himself by lending it succour. Truly he is the Kremlin’s useful idiot.”

He added: “There is only one thing that gives the Kremlin succour and lends false credibility to its propaganda onslaught. That is when politicians from the targeted countries join in.

“Sadly, I am driven to the conclusion that Jeremy Corbyn has joined this effort.”

Skripal attack aftermath – in pictures Show all 15 1 /15 Skripal attack aftermath – in pictures Skripal attack aftermath – in pictures Scene of attack Members of the emergency services in hazard suits fix the tent over the bench where Sergei and Yulia Skripal were found unconscious on a park bench in Salisbury in March 2018. Getty Skripal attack aftermath – in pictures Victim - Sergei Skripal The retired Russian colonel and former double agent for MI6 was in a critical condition in hospital for more than two months after being exposed to novichok in Salisbury. He was given refuge in the UK after being jailed in Moscow for treason. Mr Skripal came to Britain as part of a high-profile “spy swap” in 2010 in which four men were exchanged for ten Russian "sleeper agents" in the US. In this image he is speaking to his lawyer from behind bars in Moscow in 2006. AP Skripal attack aftermath – in pictures Victim - Yulia Skripal Yulia Skripal was struck down by a novichok poison alongside her father Sergei. Facebook Skripal attack aftermath – in pictures Scene of attack A police officer stands guard outside a branch of the Italian chain restaurant Zizzi where the pair dined at before falling ill. It was boarded off whilst investigators worked on the building and later found traces of the chemical weapon within it. AFP/Getty Skripal attack aftermath – in pictures Scene of attack Large areas of central Salisbury were cordoned off by police following the discovery of the Skripals. Traces of nerve agent were also found in The Mill pub. PA Skripal attack aftermath – in pictures Victim - Nick Bailey Detective Sergeant Nick Bailey, rushed to the aid of the Russian ex-spy and his daughter who were targeted with a nerve agent. He was hospitalized after aiding them and didn't leave until three weeks after the attack. Wiltshire Police/Rex Skripal attack aftermath – in pictures Police investigation - Skripal’s home Police believe they were poisoned at home, and detectives found the highest concentration of novichok on the front door of Mr Skripal’s house. Getty Skripal attack aftermath – in pictures Theresa May visits scene of attack Britain's Prime Minister Theresa May spokes with Wiltshire Police's Chief Constable Kier Pritchard near where the Skripal's were found. Britain expelled 23 Russian diplomats over the nerve agent poisoning and suspended high-level contacts, including for the World Cup on March 14. Theresa May told parliament that Russia had failed to respond to her demand for an explanation on how a Soviet-designed chemical, Novichok, was used in Salisbury. AFP/Getty Skripal attack aftermath – in pictures Skripal days before attack Sergei Skripal days before he was exposed to Novichok, that has left him fighting for life. ITV News Skripal attack aftermath – in pictures Police investigation - military involvement British soldiers were deployed soon after the attack to help a counter-terrorism investigation into the nerve agent attack. One of the places they were asked to help out with was Skripal's home and it's surrounding. They were asked to remove a vehicle connected to the agent attack in Salisbury, from a residential street in Gillingham. AFP/Getty Skripal attack aftermath – in pictures Police investigation Personnel in protective coveralls and breathing equipment cover an ambulance with a tarpaulin at the Salisbury District Hospital. AFP/Getty Skripal attack aftermath – in pictures Police investigation The investigation extended to the grave of Sergei Skripal's son Alexander in London Road cemetery. Getty Skripal attack aftermath – in pictures Police investigation The Counter Terrorism Policing Network requested assistance from the military to remove a number of vehicles and objects from Salisbury. EPA Skripal attack aftermath – in pictures Home Secretary visits scene of attack Home Secretary Amber Rudd visited the scene of the nerve agent attack at the Maltings shopping centre on 9 March. Getty Skripal attack aftermath – in pictures Yulia Skripal speaks for the first time Yulia Skripal, speaking for the first time, said she felt lucky to have survived the nerve agent attack in Salisbury which left her fighting for life. Ms Skripal said her life had been “turned upside down” by the assassination attempt. But the Russian national added she hoped to return to her homeland one day, despite the Kremlin being blamed for the attack. Reuters

Mr Corbyn faced criticism over his response to the Salisbury attack after he demanded further evidence Russia was responsible and questioned the abilities of the UK security services.

However, Labour has claimed its caution was vindicated in recent days, when government scientists at the Porton Down research laboratory admitted they had been able to confirm the source of the novichok agent used in the poisoning.

Mr Johnson faced questions over his previous suggestion that Porton Down had told him there was “no doubt” over the source of the agent – a claim that now appears to have been inaccurate.

Jeremy Corbyn says Boris Johnson has 'questions to answer' over Porton Down Novichok claims

A Labour spokesperson said Mr Johnson had “made a fool of himself and undermined the government” with his latest comments, adding: “Jeremy Corbyn has repeatedly said the evidence points to Russia being responsible, directly or indirectly, and that the Russian authorities must be held to account on the basis of evidence.”

But other senior Conservatives backed the foreign secretary. Sajid Javid, the housing and communities secretary, told the BBC’s Andrew Marr Show: “There’s no doubt when it comes up against this issue with Russia that we are having, this very serious issue, that Jeremy Corbyn has let the British people down.”

Sergei Skripal, 66, and his 33-year-old daughter Yulia were found unconscious on a park bench in Salisbury on 4 March.

Following confirmation that the former MI6 spy and his daughter had been poisoned with the novichok nerve agent, the UK government blamed Russia for the attack and announced a new of spate of sanctions against Moscow, including the expulsion of 23 diplomats. Russia has denied responsibility and said Britain must provide more evidence.

On Saturday, the Russian embassy in the UK said its ambassador had requested a meeting with Mr Johnson to discuss the case and called recent communication between the two governments “utterly unsatisfactory”. It expressed hope the UK would “engage constructively” with the request, but the Foreign Office dismissed the move as a “diversionary tactic”.