British police are investigating a suspected plot to kill a former Russian spy by poisoning him. Exiled agent Alexander Litvinenko, an outspoken critic of Russian President Vladimir Putin, on Sunday (November 19), was in "serious but stable" condition, a police spokesman said. After visiting him, close friend Alex Goldfarb said he looked like a ghost. "I saw him yesterday and he looks like a ghost. He lost all his hair, he has a red mouth because he has an inflammation in his mouth. He looks like a cancer patient who went through heavy chemotherapy. And just a month ago he was a fit, young, handsome guy," Goldfarb told journalists outside the London's University College hospital. Goldfarb said doctors felt his chances for survival were 50-50 and they were convinced that poison used was thallium. "Yes, they are hundred percent sure that this is thallium, in his blood are three times the acceptable level and there is no doubt that he has been poisoned because this kind of thing you wouldn't commonly find around," he continued. In a murky tale that could have come straight from the pages of a Cold War spy novel, Litvinenko said he fell ill after meeting a contact while investigating the Moscow murder of Russian journalist Anna Politkovskaya. "I do feel very bad. I've never felt like this before -- like my life is hanging on the ropes," Litvinenko told The Sunday Times newspaper from his hospital bed. "When I saw him I thought that they finally got him, as they have been threatening for the past seven years when he started ... started irritating the Russian government and the Russian secret services with his work and his statements," Goldfarb told journalists. Scotland Yard police headquarters refused to go into details but a spokeswoman said: "Officers from the specialist crime directorate are investigating a suspicious poisoning. No arrests have been made. Inquiries are continuing." Media reports said Litvinenko had been poisoned with the deadly chemical thallium which is used in rat poisons and insecticides. It has earned the macabre nickname "inheritance powder". Thallium attacks the nervous system lungs, heart, liver and kidneys. The colourless, odourless toxin results in hair loss, vomiting and diarrhoea. One gram can be enough to kill. Litvinenko, a former colonel in the Russian secret service, fell ill earlier this month after having lunch in a sushi bar with a mysterious contact known only as Mario. "I ordered lunch but he ate nothing. He appeared to be very nervous. He handed me a four-page document which he said he wanted me to read right away," Litvinenko told the paper. "It contained a list of names of people, including FSB (Federal Security Service) officers, who were purported to be connected with the journalist's murder," he added. Litvinenko said: "They probably thought I would be dead from heart failure by the third day." Politkovskaya, who had criticised Kremlin policy in the troubled Chechnya region, was shot dead by an unknown gunman in her apartment building on October 7. Politkovskaya, a mother of two, was well-known for exposing rights abuses by Russian troops and remained critical of Moscow's campaign despite intense government pressure. Bulgarian dissident Georgi Markov was murdered in London with a poison-tipped umbrella in 1978, at the height of the Cold War.