The Russian authorities yesterday stood accused of orchestrating a campaign of intimidation against British interests in Moscow, where the ambassador has been harassed and the BBC Russian Service mysteriously taken off air.

With ties between the Kremlin and London already strained by the police inquiry into the murder of Alexander Litvinenko, The Times has learnt that relations with Russia risk being further damaged by other serious diplomatic disputes.

The Foreign and Commonwealth Office (FCO) said yesterday that it had complained to the Russian Ministry of Foreign Affairs over the treatment of Tony Brenton, the British Ambassador in Moscow.

Mr Brenton has been the target of intimidation for the past four months by Nashi, a right-wing youth movement connected to the Kremlin. The group has trailed and heckled the envoy, picketed the embassy and triggered a violent incident outside his residence in September. There are fears for the safety of Mr Brenton and his family.

On Monday a protester shouted “Brenton apologise!” when the ambassador was taking part in a seminar at the Humanities University in Moscow with Tom Stoppard, the British playwright.

“It is a deliberate psychological harassment which is done professionally and which borders on violence,” Mr Brenton said.

The FCO said that it had been assured that concerns about the ambassador’s safety would be “addressed urgently” by the Russian authorities. But a Russian Foreign Ministry spokesman said later that the protests were lawful and protected by the country’s right to freedom of speech.

Privately British officials suspect that the entire campaign is being co-ordinated with elements inside the Russian regime angered by the ambassador’s speech to an opposition meeting in July.

At the time President Putin accused Mr Brenton of interfering in Russia’s domestic affairs, after the envoy spoke at the Other Russia opposition gathering held before the G8 summit in St Petersburg.

The Russians are also suspected of a hand in the disruption of the BBC’s Russian Service FM broadcasts in Moscow and St Petersburg, at the height of coverage of the Litvinenko poisoning.

The daily four-hour transmissions went off air in St Petersburg from November 13 to December 1, the period when the poison story broke, Litvinenko died and, in a final statement, accused Mr Putin of his murder.

In Moscow the broadcast went off air on November 24, the day after Litvinenko’s death, and has not resumed since. Sarah Gibson, the head of the BBC Russian Service, said that this was the first time that the FM transmissions had been stopped. She said that the Russians had blamed “technical difficulties” for the suspension.

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