LONDON­ — Scotland Yard has formally accused Russia of carrying out a nuclear attack on the streets of London for the first time.

Years of painstaking investigation and forensic work have convinced British law enforcement agents and the security services that the Kremlin was behind a dastardly plot to assassinate a Russian defector with a cup of tea laced with the radioactive isotope Polonium-210.

“Our silence must now end,” said the lawyer representing Scotland Yard, on the penultimate day of the inquiry into the death of Alexander Litvinenko.

Litvinenko, a former KGB and FSB agent, died slowly, and in great pain, in November 2006. Several weeks earlier he had taken tea with a former Russian intelligence operative at a luxury hotel less than a mile from Buckingham Palace.

The radioactive substance that killed him was eventually detected in hair samples and traced, via a teapot at the Millennium hotel, all the way back to Moscow.

“The… investigation has always had, at its central core, the science,” said Richard Horwell QC, representing Scotland Yard.

He explained that the radioactive trail proved Dmitri Kovtun, a former Soviet army officer, and Andrei Lugovoi, a retired FSB agent, had been the men who administered the fatal dose of nuclear poison. Their attempt to evade the authorities using such a rare murder weapon backfired spectacularly.

“It is the scientific evidence that condemns Lugovoi and Kovtun,” Horwell told the inquiry “No matter how many state honors Putin may pin to Lugovoi’s chest for services to the motherland, however meteoric Lugovoi’s rise in politics has been and may become, however many times Kovtun promises to blow apart this inquiry, Lugovoi and Kovtun have no credible answer to the evidence and to the trail of polonium they left behind.”

Litvinenko, 43, had been working for Britain’s foreign intelligence agency, MI6, supplying information about the Russian security services for three years. After securing asylum in Britain, he had also renewed his attacks against Vladimir Putin.

In 1999, he wrote a book claiming that an FSB “false flag” operation had carried out the firebomb attacks on Russian apartment bombings that killed 300 and paved the way for Russia’s war in Chechnya. He also claimed Putin had links to Russian organized crime and accused him of ordering the murder of campaigning journalist Anna Politkovskaya.

“The evidence suggests the only credible explanation is that in one form or another the Russian state was involved in Mr. Litvinenko’s murder,” Horwell said. “The two attacks on Mr. Litvinenko were an outrage. They led to great suffering on his part and eventually to his demise.”

British officials also believe the plot to bring radioactive substances into London could have endangered many more lives. Traces of polonium were found all over the city where Lugovoi visited, including a lap-dancing club and the Arsenal soccer stadium.

“We will never know how dangerous the exposure of polonium to the public at large will be and what long-term effects will be visited upon Londoners,” said Horwell.