Investigators outside the Zizzi restaurant in Salisbury, where the pair are believed to have dined before falling ill Credit:Eddie Mulholland For The Telegraph Police on Wednesday said government scientists had identified the nerve agent used by would-be assassins at a shopping arcade in the Wiltshire city centre. The chemical used is “likely to be rarer than Sarin or VX nerve agents”, a source told the BBC. Access to such toxins are tightly regulated, meaning the Salisbury plot would have taken considerable planning to execute.Hamish de Bretton-Gordon, a former commanding officer of Britain’s Joint Chemical, Biological, Radiological and Nuclear Regiment, told The Times: “This is not the stuff you can knock up in your back shed.”It is quite challenging to make. The inference is that this has probably come from a major laboratory, probably state-run.”Police: Spy and daughter ‘targeted specifically’Assistant Commissioner Mark Rowley, the head of counter-terrorism policing, revealed on Wednesday that the incident was being treated as attempted murder and the pair had been “targeted specifically”. Mr Rowley reiterated his appeal for anyone who was in Salisbury city centre on Sunday to come forward to help with the “missing pieces” in the case.Dame Sally Davies, the chief medical officer, said the incident posed a “low risk” to the public and advised that all the sites the pair were known to have visited had been “secured”. Emergency workers wear protective equipment in Salisbury at one of the scenes of investigation of the nerve agent attackCredit:Peter Macdiarmid/LNP Russia denies responsibility for Salisbury attackRussia has denied responsibility for the attack, which comes seven years after Mr Skripal was released from the country as part of a spy swap with the US.He had been convicted in his home country in 2006 for passing state secrets to MI6. Ms Rudd told MPs: “There will come a time for attribution and there will be, then, consequences and there will be further information that follows.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. While Mr Williamson refused to say if he held Russia responsible for the attack in Salisbury, he described the attempted murder of Sergei Skripal and his daughter as “absolutely disgusting”. “Of course he’s very anxious, he’s very concerned. He did his very best on that night.”All of our staff that attended the incident in Salisbury in the Maltings, they performed the role that police officers and police staff do every day up and down the country. Limited information, responded to try and protect people and safeguard people who we knew were ill.”I’m massively proud of what Nick did and all of my staff on that night, they did a first-class job.”Sgt Bailey was one of the first to go to the aid of the Skripals, who were found slumped on a bench on Sunday afternoon.He is much-loved by colleagues, many of whom have paid tribute to their “courageous” friend. Boris Johnson, the Foreign Secretary, earlier described the events as “very troubling”. He said: “If this does turn out to be in any way the result of hostile activity by another government, or directed, led, by another government, then the people of this country can be absolutely sure that the UK will respond robustly.” Police Sergeant Nick Bailey has been named as the officer who was injured with a nerve agent as he attended the scene where Sergei Skripal and his daughter Yulia were poisoned.He was hospitalised after attending to the pair and is now thought to be awake and engaging with medical staff, although he remains in a serious condition.Sgt Bailey was highly commended in 2016 for his work in putting a serial rapist behind bars.He worked tirelessly for two years in order to build a case against Arthur Bonner, who sexually assaulted multiple victims over four decades between the early 1970s and 2014. Sgt Bailey received the Chief Constable’s Certificate of Excellence for his work at the time.Kier Pritchard, temporary chief constable of Wiltshire Police, said: “I did go and see Nick today and I met Nick and his wife at the hospital in the intensive care unit.”I’ve known Nick for many years, he’s a great character, he’s a huge presence in Wiltshire Police – well liked, well loved, a massively dedicated officer. He’s clearly receiving high specialist treatment.”He’s well, he’s sat up. He is not the Nick that I know but of course he’s receiving a high level of treatment. He’s in the safe hands of the medical professionals working in Salisbury District so I’m very confident he’s getting the best professional support that he can. Investigators continue to work at ones of the scenes in Salisbury on WednesdayCredit:Paul Grover for The Telegraph Sergei Skripal and his daughter Yulia, who are seriously ill in hospital, in a restaurant believed to be in Salisbury Sergei and Yulia Skripal remain in a serious condition in intensive care after being poisoned in Salisbury Meanwhile, Amber Rudd has promised to bring those behind the attempted murder of Col Skripal to justice “whoever they are and wherever they may be” as MPs accuse the Kremlin of a “brazen act of war”.The Home Secretary described the poisoning of Col Skripal and his daughter as a “reckless” crime, adding that it was conducted in the “most cruel and public way”.It came as former minister Sir Edward Leigh said the circumstantial evidence against Russia was “very strong”, warning that if the Kremlin were implicated it would be an act of war aimed at “humiliating our country”. He declined to specify the nerve agent or how it was administered.Mr Rowley said: “Having established that a nerve agent was the cause of the symptoms, leading us to treat this as attempted murder, I can also confirm that we believe the two people who originally became unwell were targeted specifically.”Our role now of course is to establish who is behind this and why they carried out this act.”Video: Mark Rowley’s statement outside Scotland Yard Ms Rudd said more details about the nerve agent would not yet be made public, but told BBC Radio 4’s Today programme that it was “very rare”.PM: Poisoning is appalling and reckless crimeDowning Street said Theresa May was being kept updated by officials on developments in the Salisbury case.The Prime Minister’s official spokesman said: “It’s clear that this was an appalling and reckless crime and the public will rightly want those responsible to be identified and held to account.”But it is important that we avoid speculation and allow police and others to rigorously establish the full facts.”As the Home Secretary and Foreign Secretary have made clear, our response to those found to be responsible will be robust.”The spokesman said Mrs May sent her personal thanks to police and emergency workers for their courage in responding to the incident, and also wished to thank the people of Salisbury.Video: Amber Rudd gives update on poison victims The investigation has triggered a diplomatic row and prompted crisis talks in Whitehall, but Ms Rudd said police must respond to “evidence, not to rumour”. Ms Rudd declined to say whether she regarded Russia as responsible for the Salisbury attack, but said the Government will put a plan in place to respond when the culprit is identified. Questions have been raised about the deaths of both Col Skripal’s wife, Luidmila, and his son, Alexander, following the attempted murder of the former double agent.Mrs Skripal died of cancer in 2012 aged 59. His son, who was 43, died in St Petersburg last July and is commemorated with a plaque at the cemetery.It has been reported that both Col Skripal and his daughter, Yulia, who are now both fighting for their lives in hospital, visited the site last week, leaving flowers to mark what would have been Mr Skripal’s 44th birthday.A cemetery worker told The Mirror: “I recognised him. He regularly came to visit the grave and also his wife’s grave. It’s so sad.” Ms Rudd added: “Let me be clear, we are absolutely robust about any crimes committed on these streets of the UK. There is nothing soft about the UK’s response to any sort of state activity in this country.”You may not hear about it all, but when we do see that there is action to be taken, we will take it.”Nerve agent ‘rarer than Sarin or VX’Hundreds of detectives, forensic officers and analysts are working on the case, which has drawn comparisons to the poisoning of former Russian intelligence officer Alexander Litvinenko on British soil in 2006. “When we have all the evidence of what took place, we will – if it is appropriate – attribute it to somebody,” the Home Secretary told BBC Radio 4’s Today programme.”If that is the case then we will have a plan in place. We need to be very methodical, keep a cool head and be based on the facts, not rumour.”Video: Sergei Skripal days before he was poisoned Listing examples of Russian aggression in eastern Europe and its involvement in the conflict in Ukraine, Mr Williamson added that there was an urgent need to counter the Kremlin’s “increasingly aggressive stance”.”Russia’s changing the way they actually fight and raise the level of conflict,” he told BBC Radio 4’s Today programme. “We are seeing this in the north Atlantic as well – the amount of submarines that are operating, there’s a 10-fold increase in the last seven years.”Russia’s being assertive, Russia’s being more aggressive, and we have to change the way that we deal with it because we can’t be in a situation in these areas of conflict where we are being pushed around by another nation.” The targets of the attempted murder – Col Skripal, 66, and his 33-year-old daughter Yulia – remain in a serious condition in intensive care. They are understood to both be in comas.He was among the first to go to the aid of the pair, who were found slumped on a bench on Sunday afternoon.The disclosure of the officer’s poisoning will add to growing pressure on the Government to take a hardline approach against Russia if state involvement is confirmed. This morning, Amber Rudd, Home Secretary, said he was “talking and engaging”.She said: “I’m more optimistic for him, but it’s too early to say. This is a nerve agent. “You know, we are still treating it as very serious.”Part of a cemetery where the wife of former Russian spy Sergei Skripal is buried has been cordoned off by police.Officers were guarding London Road cemetery in Salisbury, Wilts, on Tuesday morning, when it was partly closed to the public and seal off with police tape. The cordon around the spy’s house, some two miles away, has also been widened. Thank you for the huge number of messages of support for our injured officer in hospital. We all wish for a full and speedy recovery #proud— Kier Pritchard (@wiltspoliceCC) March 8, 2018 A key focus will be working to uncover the origin of the nerve agent.The BBC reported that a source familiar with the investigation said it was “likely to be rarer than Sarin or VX nerve agents”.Nerve agents, which are chemical weapons, have been used in assassinations and attacks in war zones in recent years.Kim Jong-un’s half-brother Kim Jong-nam was killed at an international airport in Malaysia last year in an attack using a nerve agent known as VX.Another well-known nerve agent, Sarin gas, killed more than 90 people in a rebel-held area in Khan Sheikhoun, Syria, drawing international condemnation of the Bashar Assad regime. “The use of a nerve agent on UK soil is a brazen and reckless act. This was attempted murder in the most cruel and public way. People are right to want to know who to hold to account.”But if we are to be rigorous in this investigation, we must avoid speculation and allow the police to carry on their investigation.”We are committed to doing all we can to bring the perpetrators to justice, whoever they are and wherever they may be.”The investigation is moving at pace and this Government will act without hesitation as the facts become clearer.”It comes after the Defence Secretary Gavin Williamson said Britain must put up a stronger front against Russian military aggression as he warned that “we are being pushed around” by the Kremlin. As suspicions deepen over Russia’s potential involvement in the poisoning, Gavin Williamson said that Vladimir Putin’s regime posed an “ever-greater threat”.His warning comes after a police officer poisoned by a “very rare” nerve agent in Salisbury while going to the aid of Col Skripal and his daughter was said to be “talking and engaging” in hospital, according to the Home Secretary.