"Such actions by the UK representatives contradict the international practice of performing such inspections," Aeroflot pointed out, adding that it is ready to cooperate with Britain if it justifies and explains its actions.

The chairman of the Russian State Duma's Transport Committee, Vitaly Yefimov, also called the actions of British authorities "illegal" and said they violated international regulations.

"The board of the airplane is the territory of Russia, just like its embassy," Yefimov told Tass. "It is a precedent... It's the first time on my memory when the authorities go in and inspected an aircraft with no justification. They have no right to do it."

An inspection of a plane can only be carried out in agreement with the crew, the MP stressed, adding that he's waiting for official explanations from the British.

The Russian aviation security center will send a request to the UK authorities regarding searches of the Aeroflot plane in London, the Russian Transport Ministry said in a statement. In the event that the British side fails to provide any explanations, Moscow "will regard these actions against our plane as illegal, and will consider similar measures against British aircraft," it added.

Deputy Chairman of the State Duma's Committee for Security, Anatoly Vyborny, blasted the search of the Russian plane as "legal nihilism" and a "flagrant violation of the norms of international law" on the part of Britain.

This failure to keep the Skripal family in Russia properly informed of Sergey and Yulia Skripal's condition and of the taking of blood samples from them, is matched by the refusal of the British authorities to allow the Russian authorities consular access to them notwithstanding that Yulia Skripal is a Russian citizen not a British citizen (the Russians say that Sergey Skripal has dual nationality and is also a Russian as well as a British citizen).

This is despite the fact that both a bilateral treaty - the 1965 Consular Convention between Britain and the USSR (of which Russia is legally the successor state) - and an international treaty - the 1963 Vienna Convention on Consular Relations - both appear to require the British authorities to grant consular access to the Russian authorities to Russian citizens such Yulia Skripal who find themselves in difficulties in Britain.

The expulsion of 105 Soviet diplomats, journalists and trade representatives by the Heath government in 1971 is the single biggest action taken against Moscow by any western government. Sir Alec Douglas-Home, then foreign secretary, was accused by Labour of over-reaction. Many were exposed by Oleg Lyalin, the first Soviet intelligence agent to defect since the second world war. Oleg Gordievsky, who later defected from the KGB, said the expulsions dealt a heavy blow to the Soviet Union's intelligence effort here. Moscow responded by expelling 18 British embassy staff from Moscow.