Russian State television has reported that British embassy officials were using a transmitter inside a fake rock to try to secure state secrets.
A spokesman for the state FSB security service confirmed the television pictures and said, using jargon that implied spying: "The diplomats were shown to be involved in activities that were incompatible with their diplomatic status."
On Sunday, Russian state television broadcast footage of what it said were British diplomats spying through a transmitter in an imitation rock on a street in Moscow and then downloading classified information from it.
The report said at least part of the footage was shot in autumn last year.
The programme said one embassy employee had been authorising regular payments to Russian non-governmental organisations.
Earlier this month, Vladimir Putin, the Russian president, signed into law legislation on registering NGOs which Western critics say will seriously curb the activities of one of the few areas of public expression that remains outside Kremlin control.
A TV grab showing an X-ray of
the transmitter in the rock
In London, the foreign office said: "We are concerned and surprised at these allegations. We reject any allegation of improper conduct in our dealing with Russian NGOs.
"It is well known that the UK government has financially supported projects implemented by Russian NGOs in the field of human rights and civil society."
A British embassy spokesman declined to say whether the diplomats named in the broadcast were still in Russia.