The Russian security service, the FSB, last night named as spies four employees of the British embassy in Moscow, showing them on state television allegedly collecting intelligence using hi-tech gadgets and funding non-governmental organisations (NGOs).

It marks the Putin administration's most bold attempt to expose western intelligence work in Russia. The FSB caught the unit late last year, a documentary on state-run Rossiya TV reported. An FSB spokesman confirmed to the Guardian that his agency had accused the four men of being spies. "They have not been arrested. How could we? They are all diplomats." He declined to say what information they had tried to acquire. "They used hi-tech, new gadgets to communicate with [Russian] agents, with citizens of another country who gather intelligence."

According to a report of the programme from the state RIA Novosti agency, two men, aged 30 and 32, were named as spies. A third diplomat named as a spy was an aide to MI6's Moscow desk officer, the only MI6 agent officially declared to the FSB, and a fourth had a role in funding Foreign Office projects.

The programme focused upon an alleged secret transmitter hidden in a square in central Moscow. The FSB officer said: "At first we thought it was a classic drop point - a container camouflaged with a stone. Then ... it became clear there was an electronic device inside it." They said the stone contained a battery and a device to transmit and receive. It had been fastened into the walls using wooden screws and sealed to make it watertight.

The programme described how Russian agents for MI6 and the British diplomats communicated by passing by the stone with a PDA handheld computer which would send or receive data from the device inside at up to 20 metres.

The FSB officer said the device did not work properly, causing the four diplomats to visit the square regularly in the autumn. One diplomat was filmed dressed "as a student", a rucksack on his back. A Russian had been caught using the stone and later admitted to spying. One diplomat, 27, educated at a university in the north of England, was named as the recruiter for MI6 agents. The programme said his work put him in contact with many NGOs. The FSB officer showed paperwork he claimed proved this diplomat had funded several Russian NGOs. One paper, apparently dated last week, gave a media organisation £5,719 to produce a newspaper.

The focus comes just after the Kremlin rushed into law a bill that NGOs say will hamper their work. The Kremlin says NGOs are a front for spying; last year the FSB accused the British medical relief charity Merlin of espionage, a claim it firmly denies.

The British embassy in Moscow declined to comment. In London, the Foreign Office said: "We are surprised at these allegations. We reject any allegation of improper conduct in our dealings 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." Allegations about British intelligence, notably MI6, are invariably met with a response that the government never comments on intelligence matters.

Backstory

Vladimir Putin's administration has in recent years cracked down on potential fronts for espionage, prompting accusations of renewed cold war-esque spy fever from the security services, the FSB. Increased counter-intelligence, though in keeping with efforts to reinforce state control, has boosted accusations of a crackdown on dissent. FSB director Nikolai Patrushev each year reveals the number of foreign spies unearthed, usually about 100. One of the four alleged British spies named had official links to NGOs, and their exposure now will prompt accusations that the timing was to justify a law signed on January 10.