Tony Brenton, Britain's ambassador to Russia, called on Moscow to take part in finding an acceptable for both countries solution to the dispute over London's demand for the extradition of a suspect in the murder of the ex-KGB agent late last year.
"We are not demanding that Russia should violate its constitution, but we propose that we should jointly look for a possibility of circumventing this obstacle," Benton told the Interfax agency.
Brenton based his remark to Moscow's main argument in refusing to extradite Andrei Lugovoi, namely constitutional grounds. Scotland Yard considers Lugovoi the chief suspect in the radioactive poisoning murder of ex-KGB agent Alexander Litvinenko in November 2006.
Brenton said he felt the Russian constitution was open to various interpretations and that in view of the serious and exceptional case of murder, the legal obstacles should be circumvented.
The British diplomat criticised the fact that so far, Russia had shown no "sufficient willingness for cooperation" in the murder case.
The ambassador's remarks come amid ongoing tensions between Moscow and London in the extradition controversy.
Just two days ago Russian Foreign Minister Sergei Lavrov said Russia is seeking to revise and amend its relations with Britain, after a week of diplomatic rows and expulsions between the two countries.
The Kremlin expelled four diplomats from the UK embassy in Moscow in retaliation for a similar move by Foreign Secretary David Miliband earlier this week. The tit-for-tat moves reminiscent of the old Cold War era caused the dispute over the extradition demand escalate.