Interpol notices and European arrest warrants have issued for the two suspects in the murder of Russian spy Alexander Litvinenko after an inquiry ruled there is "no doubt" they were responsible. The Treasury has also confirmed they have frozen the assets of Andrei Lugovoi and Dmitry Kovtun as the government consides further action against the pair and Russia.

The long-awaited report by Sir Robert Owen concludes Litvinenko was deliberately poisoned during an operation "probably" approved by Russian president Vladimir Putin and former head of the Moscow intelligence service FSB, Nikolai Patrushev.

Following the release of the report, the home secretary Theresa May said murdering Litvinenko in London and putting hundreds of others at risk of radiation poisoning was a "blatant and unacceptable breach" of international law and civilised behaviour.

Speaking in the House of Commons, May added: "We are considering the findings in detail and their implications. In particular, the conclusion that the Russian state was probably involved in the murder of Mr Litvenenko is deeply disturbing.

"It goes without saying that this was a blatant and unacceptable breach of the most fundamental tenants of international law and of civilised behaviour. We have to accept that this does not come as a surprise. The inquiry confirms the assessment of successive governments that this was a state-sponsored act."

Elsewhere, May said the Russian ambassador in London is being summoned to the Foreign Office so the government could express their "profound displeasure" to Russia regarding their actions.

David Cameron said the news Putin may have approved an act described a "nuclear terrorist attack on the streets of London" as "extremely disturbing". A 10 Downing Street spokesperson added: "It is not the way for any state, let alone a permanent member of the UN Security Council, to behave. Regrettably, these findings confirm what we and previous governments already believed."

Britain does U-Turn on Ex-KGB Litvinenko Murder Inquiry
An inquiry has found Vladimir Putin \'probably\' approved the assassination of Alexander Litvinenko Getty

Police have confirmed they are still seeking to put the two main suspects in the "cold and calculated murder" of Alexander Litvinenko before a criminal court in the UK.

Neither Lugovoi or Kovtun were present during the six-month hearings and did not give evidence as Russia refused to extradite the pair. In the years following Litvinenko's death in 2006, Putin "supported and protected" Lugovoi despite being named as a key suspect, including handing him an honour for services to the fatherland while the inquiry was taking place.

Lugovoi described the allegations as "absurd" and an attempt by London to "use a skeleton in the closet for the sake of its political ambitions". He added; "As we expected, there was no sensation. The results of the inquiry published today are yet more proof of London's anti-Russian stance, its blinkered thinking and ... unwillingness to establish the true cause of Litvinenko's death."

Met Police commander Duncan Ball, who led the investigation into the murder of Litvinenko, said: "This has been a painstaking and meticulous enquiry over a number of years that has brought unprecedented challenges requiring an innovative and groundbreaking investigation.

"I would like to pay tribute to the investigation team who have worked tirelessly to discover the circumstances surrounding Alexander Litvinenko's death and the identity of those responsible. Without their efforts, this murder and the use of Polonium 210 as a weapon would have gone undetected and the public left at greater risk."