With permission, Mr Speaker, I shall make a statement on the incident in Salisbury that has been unfolding over the past four days.Let me first pay tribute to the continued professionalism, dedication and courage of the emergency services. They have handled the incident with their customary attentiveness, alacrity, and sense of public duty. First responders put themselves in dangerous situations on a day-to-day basis, and this incident has underlined that fact – to which, sadly, I shall return later in my statement.I shall now update the House as far as is possible on the basis of the current facts of the case. At approximately 4.15pm on Sunday afternoon, Wiltshire police received a call from a member of the public who was concerned for the welfare of two people in a park in Salisbury. Emergency services were called, and the two were admitted to the A&E department of Salisbury District Hospital. They were a man in his 60s and a woman in her 30s, with no visible signs of injury. They are understood to be Sergei and Yulia Skripal. Both remain unconscious, and in a critical but stable condition.I regret to inform the House that a police officer has also fallen seriously ill. The officer was one of the first responders on Sunday, acting selflessly to help others. The latest update from the hospital is that the officer’s condition remains serious but stable, and that he is conscious, talking and engaging. Officers from Wiltshire police are providing support for the officer’s family and colleagues. Our thoughts are with all three victims, and their families and friends, at what will be an incredibly difficult time for them.Wiltshire police began an investigation on Sunday to determine how the individuals had fallen ill, and whether a crime had been committed. They declared a major incident on Monday. On Tuesday the Metropolitan police decided that, given the unusual circumstances, responsibility for the investigation should be transferred to the National Counter Terrorism Policing Network. Samples from the victims have been tested by experts at the Defence Science and Technology Laboratory at Porton Down, who are world-renowned experts in the field. As Assistant Commissioner Mark Rowley announced yesterday, that forensic analysis has revealed the presence of a nerve agent, and the incident is therefore being treated as attempted murder. I can confirm that it is highly likely the police officer has been exposed to the same nerve agent.I spoke only this morning with Assistant Commissioner Mark Rowley, and he confirmed that we remain in the midst of a fast-paced, criminal investigation. As such, I will not comment further on the nature of the nerve agent. We must give the police the space they need to conduct a thorough investigation. All members will recognise that an investigation such as this will be complex and may take some time.Public safety continues to be the No.1 priority for this government. Professor Sally Davies, the chief medical officer, stated yesterday that, based on the evidence we have, there is a low risk to the public. The UK has a world-leading emergency response. It is regularly tested and exercised to ensure we can deliver an effective response to a wide range of chemical, biological and radiological incidents. The three emergency services are well supplied with state-of-the-art equipment to respond to such threats.The frontline response is supported by world-class scientific research and advice. This ensures that decision making on the ground, by all agencies involved, is firmly based on the available evidence. This will also support the decontamination activity needed to return the location to normality.The police are working closely with Public Health England, the Department for Environment, Food and Rural Affairs and the DSTL. They have cordoned all known sites in Salisbury that were visited by the two initial victims before they became unwell, and are taking the necessary measures to protect public safety.I want now to turn to the speculation – of which there has been much – around who was responsible for this most outrageous crime. 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.As the assistant commissioner said yesterday, the investigation now involves hundreds of officers, following every possible lead to find those responsible. Some of those leads have come from members of the public. I would like to thank the people of Salisbury for their help and for the calm they have shown over the last four days. I encourage anyone who visited Salisbury town centre and surrounding areas on Sunday afternoon, who has not yet spoken to the police, to get in touch.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. As my right hon. Friend the Foreign Secretary made clear on Tuesday, we will respond in a robust and appropriate manner once we ascertain who was responsible.I would like to close where I began, by expressing my sincere thanks to the emergency services and hospital staff for their tireless efforts over the last four days. They have acted with utter professionalism both to minimise the risk to the wider public and to care for the victims of the attack, for which I know we are all very grateful. Our thoughts will be with the victims and their families over the coming days.Finally, I thank members for their understanding that there will clearly be limits on what we can say as this investigation continues. As and when information can be made public, it will be. I commend the statement to the House.