A former UK government official has admitted Britain was behind a plot to spy on Russians with a device hidden in a fake rock, it has emerged.
Russia made the allegations in January 2006, but they were not publicly accepted by the UK before now.
Jonathan Powell, then prime minister Tony Blair's chief of staff, told a BBC documentary: "The spy rock was embarrassing.
"They had us bang to rights. Clearly they had known about it for some time and had been saving it up for a political purpose."
Six years ago, Russian state television broadcast a film claiming British agents had hidden a sophisticated transmitter inside a fake rock which was left on a Moscow street.
Embassy officials then allegedly downloaded classified data from the transmitter using palm-top computers.
The Russian security service, the FSB, linked the rock with claims that British security services were making covert payments to pro-democracy and human rights groups.
Then president Vladimir Putin later introduced a law restricting non-governmental organisations (NGOs) from getting funding from foreign governments, causing many to close down.
After the broadcast Mr Blair refused to comment on the crisis, and the Foreign Office denied any improper relations with Russian NGOs.
The documentary series, Putin, Russia and the West, will be screened on BBC Two.