The police cordon in MayfairCredit:Keith Larby/Alamy 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. “The woman came out of the restaurant and saw he needed help and rushed back in to raise the alarm,” they said. “Some members of staff came out and tried to help and someone called an ambulance, but it was clear he was already dead. “The woman then called a man who I assume was her husband who came up the road on foot and they were talking Russian.”Officers quickly widened the cordon and man whose driver is believed to have died later walked up to the police tape to look at the scene but declined to answer questions when approached by The Telegraph.Witnesses described the driver as a man between 50 and 60 and ‘quite clearly overweight’. A driver has died in an affluent street in the West End sparking fears of a copycat Salisbury poisoning as police scrambled specialist officers to deal with what was initially believed to be a Russian-linked chemical attack.Dozens of police cars and ambulances descended upon Albemarle Street in Mayfair on Thursday afternoon and a large part of the street was cordoned off.The man, believed to work for a Russian couple, fell ill while sat in a black Mercedes outside an exclusive restaurant.One workman who witnessed the events unfold said that as soon as the police arrived everyone that was in the vicinity was moved away from the car and huddled together down the street. “They told us it was suspected chemical warfare and asked if any of us had had any contact with the man who had died,” he said. “The only person who had was a man in a white waistcoat who I think was a waiter at the restaurant who gave him CPR. “They later told us that they did not believe it was a chemical attack, but I overheard one of the ambulance crew saying it was all due to his links with Russia.” A Scotland Yard spokesman said: “At approximately 15:15hrs on Thursday, 21 June, police responded to a call from the London Ambulance Service (LAS) relating to a man taken ill on Albemarle Street in Mayfair.”Officers attended the scene. At the location they found a man being treated by the LAS. He was subsequently pronounced dead at the scene.”Due to concerns the victim may have been exposed to a poison, specialist officers attended but found no evidence that would indicate the victim had been poisoned. “There are no other reports of people being taken ill. Cordons were put in place around the area to allow the emergency services to carry out their work.”A London Ambulance Service spokeswoman said: “We were called at 3.14pm today to Albemarle Street, Mayfair, to reports of a person in cardiac arrest. “We sent a number of resources to the scene with the first of our medics arriving in five minutes. Sadly, despite our efforts, a man died at the scene.” An onlooker said they saw the man – thought to be a couple’s driver – collapse at the wheel of a black Mercedes which was parked outside of the Oswald’s private members club.