Britain on Friday dismissed as “completely baseless” accusations by Russia that six UK diplomats in Moscow were spies.
The Foreign Office issued a statement after the Russian authorities revoked the accreditation of the six diplomats following espionage claims by the FSB security service.
“The accusations made today by the FSB against our staff are completely baseless,” said the FCO.
It added: “The Russian authorities revoked the diplomatic accreditation of 6 UK diplomats in Russia last month, following action taken by the UK government in response to Russian state directed activity across Europe and in the UK.
“We are unapologetic about protecting our national interests.”
The FSB alleged that the activities of the British diplomats threatened Russia's security.
The row came as Sir Keir Starmer arrived in Washington for talks with Joe Biden on allowing Ukraine to fire missiles supplied by the West deep into Russia.
Ukraine’s president Volodymyr Zelensky has been pleading for permission for this use of long range missiles from Nato countries, including Britain’s Storm Shadows.
Kyiv could use the missiles to target Russian bases from where aircraft are flying to launch “glide bombs” at cities and towns in Ukraine with devastating impacts.
Vladimir Putin has warned the West against given such consent for its missiles, arguing it would mean Nato would be at war with Russia.
But the British Prime Minister has stressed that Ukraine has the right to defend itself against the Russian invasion launched by Putin in February 2022.
Security experts say the Russian president is likely to respond to the West easing restrictions on the use of its missiles and the espionage accusations against the British diplomats may be linked to this growing clash.
Lord Peter Ricketts, a former UK national security adviser and top diplomat, said the spying claims were “Russian punishment for the UK being seen as a cheerleader for supplying weapons to Ukraine”.
Speaking to BBC radio, he said: “We’re told the Russian spy agency has documents from a department in the Foreign Office, which say that the task of the embassy is ensuring Russia’s strategic defeat against Ukraine.
“Well, surprise, surprise.”
The FSB, the main successor agency to the Soviet KGB, said it had documents showing that a British foreign office department in London responsible for Eastern Europe and Central Asia was coordinating what it called "the escalation of the political and military situation" and was tasked with ensuring Russia's strategic defeat in its war against Ukraine.
"Thus, the facts revealed give grounds to consider the activities of British diplomats sent to Moscow by the directorate as threatening the security of the Russian Federation," the FSB said in a statement.
"In this connection, on the basis of documents provided by the Federal Security Service of Russia and as a response to the numerous unfriendly steps taken by London, the Ministry of Foreign Affairs of Russia, in co-operation with the agencies concerned, has terminated the accreditation of six members of the political department of the British Embassy in Moscow in whose actions signs of spying and sabotage were found," it said.
The six diplomats were named on Russian state TV, which also showed photographs of them.
"The English did not take our hints about the need to stop this practice (of carrying out intelligence activities inside Russia),so we decided to expel these six to begin with," an FSB employee told the Rossiya-24 state TV channel.
The FSB said Russia would ask other British diplomats to go home early if they were found to be engaged in similar activity.
Russian Foreign Ministry spokeswoman Maria Zakharova was cited by the state TASS news agency as saying the activities of the British embassy in Moscow had gone well beyond diplomatic convention and accusing it of carrying out deliberate activity designed to harm the Russian people.
Britain, the US, Ukraine and its other allies have been engaged in an information war with Russia over the conflict so their statements need to be taken with caution.
But they are far more believable than the propaganda and false claims by Putin’s regime.
If British diplomats are expelled it is likely to lead to a tit-for-tat response for Russian envoys in London.
Sir Keir’s visit to Washington follows Foreign Secretary David Lammy’s trip to Kyiv alongside US Secretary of State Antony Blinken.
Neither man was drawn on granting Ukraine permission to use the long-range missiles supplied by the West to attack targets in Russia, which is a key request of President Volodymyr Zelensky.
Concern about escalation has been one of the reasons why permission has not yet been given to Kyiv.
Iran has been hit with sanctions by the UK and US after the two countries formally accused Tehran of supplying ballistic missiles to Russia.
Mr Lammy and Mr Blinken announced further financial support for Ukraine, including a £600 million package from the UK and 717 million dollars (£550 million) from the US to meet immediate humanitarian, energy and stabilisation needs.
Meanwhile, the chairman of Russia’s State Duma, the lower house of parliament, on Friday accused NATO of being a party to military action in Ukraine, suggesting it was already heavily involved in military decision-making.
Vyacheslav Volodin, a close ally of Putin, accused the US-led military alliance of helping Ukraine choose which Russian cities to target, of agreeing specific military action, and of giving Kyiv orders.
“They are waging war with our country,” said Mr Volodin.
Nato and Kyiv have made clear that Ukraine is running its military campaign against Putin’s invasion, with Western countries sometimes unaware of Ukraine’s plans.
Ukraine's air force said on Friday it shot down 24 of 26 Russia-launched drones overnight over five Ukrainian regions.
