Ben Emmerson QC told the chairman of the inquiry, Sir Robert Owen, that the evidence proves not only that the two key suspects were responsible but that the Russia state supported them.

In a long address, he explained how an extensive trail of polonium left after Mr Litvinenko's death followed exactly a route taken by Andrei Lugovoy and Dmitry Kovtun, who the Met Police believe poisoned him with the radioactive element.

Lugovoy, who Mr Emmerson said was the "general" in the operation, is now a "wealthy and heavily-protected figure in Russian politics" and was recently rewarded with a medal by Mr Putin for services to the state.

But the barrister said that equally compelling was the fact the Russia pair and state had been given ample opportunity to take part in the inquiry but had not done so.

He said: "It might be difficult for the Russian authorities to recognise an independent and impartial judicial tribunal when they see one, but the rest of the world can see the truth.

"These men, the two of them, were given repeated chances to participate, and the Russian government, either in its own capacity or through its proxy, the ICRF, had ample opportunity, both to become core participants, to provide evidence and to take a constructive part in the process.

"If the Kremlin had the slightest interest in getting at the truth, then that is precisely what the Russian authorities would undoubtedly have done.

"Instead, they have obstructed justice, destroyed evidence, rewarded murderers, manipulated the proceedings, and repeatedly attempted first to intimidate and then to smear the Inquiry.

"That approach speaks volumes and provides significant support, sir, for the conclusion that Mr Putin and his cronies were not only behind the murder but now stand foursquare behind the murderers."

Mr Emmerson spelled out in detail how large traces of polonium were found in the hotel rooms that Lugovoy and Kovtun stayed at when they came to London before visiting Mr Litvinenko.

Contamination was found in the U-bends of the sinks in their rooms, on the floor of one room and on towels which, he said, suggested there had been either efforts to dispose of the deadly substance, to transfer it, or to mop it up after a spillage.

He also said that heavy traces were found in several restaurants the pair went to, nightclubs and bars they attended, planes they travelled on, in cars they were chauffeured in and at the Emirates Stadium where they watched Arsenal play CSKA Moscow.

Before they reached the UK, polonium was found on places Lugovoy had been in Germany, including the home of his wife. 

Finally, he said, contamination was found on a toilet cubicle, door and handdryer outside the bar in the Millennium Hotel where Mr Litvinenko drank the polonium-laced tea which expert witnesses said killed him.

Shortly after, Lugovoy and Kovtun returned to Moscow.

When UK authorities tried to carry out tests on a Russian Aeroflot plane the pair had travelled in, they were told it had been taken out of service.

Mr Emmerson said the polonium undoubtedly emanated from Russia and could not have been used as a murder weapon without the knowledge of the Russian officials and the approval of Mr Putin personally.

"Secondly," he added, "the principal murderer, Andrei Lugovoy, was working closely with corrupt officials in the KGB and the Kremlin, and has been protected by state agencies ever since the murder from any form of accountability."

Also, he said there was a clear motive for Mr Putin to have wanted Mr Litvinenko dead - as the former Russian spy had not just defected and been given UK citizenship, he had provided the UK authorities with large amounts of information about the Kremlin's alleged links with organised crime.

Mr Emmerson added: "Those facts, we say, speak for themselves. No process of deduction or inference is really required.
"When all of this evidence is viewed in the round, as it must be, it establishes Russian state responsibility for Mr Litvinenko's murder beyond reasonable doubt, and if the Russian state is responsible, Vladimir Putin is responsible."

Russian presidential spokesman Dmitry Peskov said the Kremlin had no faith in the UK's inquiry into Mr Litvinenko's death.

He said: "We don't trust this. If you remember, when Litvinenko died, similar full-size accusations were made both by UK officials and agencies that were just beginning to investigate this case.

"We have already heard this and such statements were made without any results of the investigation and after the results of some investigation. To all appearances, something has to be added to consider these words as convincing," the Kremlin spokesman said.

The inquiry, which has closed for evidence after 34 days of hearing from 62 witnesses, is expected to report to the home secretary by the end of the year.