Cameron under pressure to step up sanctions on Russia
British Prime Minister David Cameron is under intense pressure to step up reprisals against Russia after Robert Owen's damning report.
Theresa May, the UK home secretary, said Mr Cameron would raise the issue with Mr Putin at the "first available opportunity".
"This was a blatant and unacceptable breach of the most fundamental tenets of international law and civilised behaviour. But we have to accept that this doesn't come as a surprise," she said.
But shadow home secretary Andy Burnham said the Government's diplomatic response did not "go anywhere near enough in answering the seriousness of the findings" and "could send a dangerous signal to Russia that our response is too weak".
He suggested the immediate expulsion of every FSB operative in the UK and strengthened economic sanctions.
The Litvinenko family barrister, Ben Emmerson QC, said the killing amounted to "nuclear terrorism", and that the family had sent ministers a list of potential targets for sanctions.
Insisting there were "always" wider political concerns that made reprisals difficult, he added: "It would be craven for the government, for the prime minister, to do nothing in response."
But the Kremlin branded the report a 'joke' and dismissed its findings as "politically motivated" and "absurd".
The report concluded that Mr Litvinenko was poisoned by Andrey Lugovoy and Dmitry Kovtun, who were probably acting under the direction of (FSB head) Nikolai Patrushev and Mr Putin when they laced 43-year-old Mr Litvinenko's tea with polonium at the Millennium Hotel in London's Mayfair.
Mr Owen said: "I am sure that Mr Lugovoy and Mr Kovtun knew that they were using a deadly poison, and that they intended to kill Mr Litvinenko. I do not, however, believe that they knew precisely what the chemical that they were handling was, or the nature of all its properties."
The report found that the two suspects had also tried to poison Mr Litvinenko at a meeting in London on October 16 - a fortnight before he ingested the fatal dose.
Other cases suggested that "in the years prior to Litvinenko's death, the Russian state may have been involved in the assassination of Mr Putin's critics", although this evidence was "circumstantial".
The use of polonium 210 was "at the very least a strong indicator of state involvement", as it had to be made in a nuclear reactor, he said.
The report details how two Scotland Yard officers who went to Moscow in search of evidence were hampered by "petty" but persistent attempts to obstruct their work.
The British Government had initially argued that a public inquiry was not necessary and the matter should be dealt with by an inquest. However, Marina Litvinenko won a court battle to have the decision overturned.
Mr Lugovoy has been "lionised' in Russia since the killing, becoming a member of the Duma, the Russian parliament, and receiving an award from Mr Putin.
Mr Owen suggested that showed Moscow was signalling approval of the murder, although he stressed that by itself did not necessarily mean the state was involved. (© Daily Telegraph, London)