An Italian intelligence expert who had lunch with Alexander Litvinenko on the day that he was poisoned was receiving emergency treatment in hospital tonight after testing positive for the same deadly radioactive isotope that killed the former Russian spy.

Mario Scaramella met Litvinenko at the Itsu sushi bar on Piccadilly on November 1, three weeks before the Russian succumbed to the radioactive toxin. Detectives investigating Litvinenko's death, who have painstakingly traced his movements that day, believe that he must have been poisoned at the restaurant.

Mr Scaramella, who has denied any involvement in the poisoning, said earlier this week that doctors had given him the all-clear. "I’m not sick, that’s for sure," he told the BBC. But sources close to the case today said that a "significant" amount of polonium-210 was found in Mr Scaramella's body.

The Home Secretary, John Reid, said this evening that a small amount of polonium had also been detected in an adult member of Litvinenko's family.

It was still unclear whether the Italian, who had not been displaying any signs of radiation poisoning, is unwell but the Health Protection Agency said that the amount of polonium discovered was enough to cause health problems.

The HPA, which has tracked contamination in the case so far, would not confirm that the second person to test positive for polonium-210 was Mr Scaramella but said the man had been "in direct and very close contact with Mr Litvinenko".

"There is likely to be concern for their immediate health," the agency said.

Mr Scaramella, who flew to London last week to help with the investigation and has been kept in a secure location outside the capital, was being treated at University College Hospital, where Litvinenko died last Thursday night.

The discovery triggered another Cobra meeting of Britain's top security officials and a health warning to the Italian Government. Mr Scaramella flew back to Rome after his meeting with Litvinenko, raising the possibility of similar low-level contamination of aircraft as has been found on flights between London and Moscow in the run-up to November 1.

"We have officially informed the Italian government because they may now need to take steps," said a spokesman for the Cabinet Office, where Cobra meets. "For example, they have the same predicament about airlines that we faced because Mr Scaramella flew out of the country."

At his lunch with Litvinenko, Mr Scaramella has said that he gave the Russian a "hit list" of planned assassinations by agents of the FSB, Russia's security service, on which both their names featured. He has said that he doubted the reliability of the information but found it alarming nonetheless.

Mr Scaramella is a professor of environmental law who worked for the Italian Parliament's Mitrokhin Commission examining KGB activity in Italy in the late 1990s. He met Litvinenko during his work for the commission and has said that the alleged hit list also included the name of Senator Paolo Guzzanti, the former chair of the investigation.