A former KGB agent, Andrei Lugovoi was named by the U.K. Crown Prosecution Service as the prime suspect in the murder of Kremlin critic Alexander Litvinenko.

Litvinenko, 43, died in London in November after being poisoned by radioactive polonium-210. UK requested Lugovoi extradition so he can stand the trial, but Russia refused to comply.

“A U.K. citizen has suffered a horrifying and lingering death,” Foreign Secretary David Miliband told Parliament in London today.

Miliband said that according to the police Lugovoi had offered tea to Litvinenko and that he later "suffered a horrifying and lingering death in front of his family. His murder put hundreds of others, residents and visitors, at risk of radiation contamination."

 “Given the seriousness of the crime, Russia's reply to the extradition request is extremely disappointing.” Miliband explained. He also said the expulsion was the "appropriate response" to Russia's lack of cooperation.

Previously Lugovoi denied the claim and under the 1957 European Convention on Extradition, Russia has the right to refuse the extradition of a citizen.

According to the convention, Britain can request the investigation to be taken on by the Russian authorities, but Sir Ken Macdonald, Britain's director of public prosecutions, has rejected an offer from the Kremlin to trial Lugovoi in Russia.

In response to Miliband’s announcement the Russian Foreign Ministry spokesman Mikhail Kamynin said that the "provocative acts will not go unanswered, and will have serious consequences for British-Russian relations."

"We would like to recall that British authorities have also recently refused to hand over citizens accused of crimes in other countries," he added.

In addition, Miliband announced that negotiations over visa relaxations for Russian citizens would also be suspended, adding that a "number of issues" regarding cooperation with Russia would need to be reconsidered.

Yesterday, Norberto Andrade, the head barman at the Pine Bar at the city's Millennium Hotel told the British newspaper that an assassin had added the lethal dose of the isotope polonium-210 to drinks that were due to be served to Litvinenko and former KGB agent Andre Lugovoi.

The barman said he had been deliberately distracted so that the killer had time to add the poison to a pot of green tea.