Russian state television has broadcast video footage of what it claims are British diplomats spying in Moscow.
In the programme, Russian intelligence officers say staff at the British embassy in the city planted a transmitter in an imitation rock on a street.
The programme also alleged that one of the embassy officials involved had been authorising regular payments to Russian non-governmental organisations.
The British Foreign Office has said it is 'concerned and surprised' at the claims and denied any improper conduct.
A spokesman said: '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. All our assistance is given openly and aims to support the development of a healthy civil society in Russia.'
'Four British diplomats are suspected. I am not ready to give their names yet, but this is all being investigated,' a Federal Security Service (FSB) spokesman told news agencies last night.
