Detectives have discovered when the former Russian spy Alexander Litvinenko came into contact with the radioactive material that was to kill him.

After retracing the route taken by Mr Litvinenko on the day he fell ill, anti-terrorist officers believe the ex-KGB agent was poisoned in or very close to the sushi bar in central London that he visited to meet an Italian contact on 1 November.

Detailed forensic analysis, including radiation testing, of the places Mr Litvinenko visited in the hours before he went to Itsu in Piccadilly have found no trace of radioactivity. This strongly suggests he was poisoned while in the restaurant, where traces of nuclear material were found.

Mr Litvinenko, 43, an outspoken critic of the Russian President, Vladimir Putin, became ill on the day he visited the sushi bar and died on 23 November from polonium-210 poisoning.

In a further development it was disclosed that extremely low-level radioactive contamination has been discovered in nine buildings, two British Airways planes which flew to Moscow, and a car used to take Mr Litvinenko to hospital. A third BA aircraft is being examined in Moscow.

The current focus of the police inquiry is what happened at the sushi bar where Mr Litvinenko met Mario Scaramella, an Italian academic who denies having anything to do with the poisoning.

Mr Scaramella, who runs an organisation that tracks nuclear waste, said earlier this week that he had been tested and was not contaminated.

Scotland Yard pinpointed the sushi bar when they traced Mr Litvinenko's movements after he left his home in Muswell Hill, north London. By using information from his mobile phone records, Oyster travel card and CCTV footage, detectives plotted his route to Piccadilly Tube station. Locations where he stopped along the way were tested for radiation contamination, but all proved negative.

As part of the inquiry detectives are testing aircraft used by several people that met Mr Litvinenko on 1 November to discover if any of them brought in radioactive material, or left Britain contaminated.

Three Russian businessmen, employees of a security company in Moscow, who met Mr Litvinenko at a hotel after he had been to the sushi bar had yesterday gone to ground. It is not clear if they were in hiding, or were being questioned by the Russian authorities.

One of the men, former FSB bodyguard Andrei Lugovoy who had known Mr Litvinenko for 10 years, was in charge of security for the former Russian prime minister, Yegor Gaidar, who was last night being treated for suspected poisoning after falling ill in Dublin.