British Aide Admits Russian Spy Claims LONDON - For the first time, a former senior official has confirmed Russian accusations that the British spy service was caught trying to use a fake rock in Moscow to hide electronic communication equipment six years ago. The Russian allegation in January 2006 came as relations between London and Moscow soured with a series of events culminating in the death in London of a former K.G.B. officer, Alexander V. Litvinenko, in November of that year. British officials later accused another former K.G.B. officer of murdering him using a rare radioactive isotope, Polonium 210. The BBC on Thursday quoted Jonathan Powell, the onetime chief of staff to former prime minister Tony Blair, as saying Russia "had us bang to rights" when Russian television ran a report showing how British diplomats used the fake rock to receive and transmit information. "Clearly they had known about it for some time," Mr. Powell was quoted as saying in an interview to be aired on television Thursday. They had been "saving it up for a political purpose," he said, according to the BBC. Footage on Russian television showed a man walking along a Moscow street, who slows his pace, glances at a rock and then accelerates, the BBC said. Then the video showed another man walking by and picking up the rock. The Russian allegation, which the British authorities declined to confirm at the time, triggered other claims by the Moscow security authorities that Britain was helping fund nongovernmental organizations opposed to Vladimir V. Putin, then the president and now prime minister. That led to a crackdown on foreign funding for nongovernmental organizations. Mr. Putin accused foreign secret services of manipulating the organizations. But Sir Tony Brenton, Britain's ambassador in Moscow at the time, was quoted by the BBC as saying Britain's relationships with the organizations were "completely above board" and "all of that was completely public." As relations soured, Britain expelled four Russian diplomats in 2007 and Moscow reciprocated with an order for four British officials to leave. Cooperation between the two countries" spy services was also suspended. Britain is still pressing for the extradition of Andrei K. Lugovoi, the former K.G.B. bodyguard it accuses of murdering Mr. Litvinenko in November 2006. Russia refuses to extradite him, saying its constitution does not permit it to hand over its own citizens. Mr. Lugovoi denies killing Mr. Litvinenko and says he was himself targeted. British Prime Minister David Cameron visited Moscow last September and said Britain's legal system did not allow it to drop its demand for Mr. Lugovoi's extradition. But, signaling a thaw, he said: ""We have a responsibility to recognize the many ways in which we do need each other, to end the old culture of tit-for-tat and find ways for us to work together to advance our mutual interests."