"Two British spies have been arrested. Of course they are not silent they are talking," Nikolai Kovalyov, the former head of the FSB, told Russia's NTV television station in a programme that will be aired on Sunday night, Interfax reported.
A spokesman for the FSB said he could neither deny nor confirm the report, advising Reuters news agency to watch the programme and listen to Kovalyov's comments.
In London, a Foreign Office spokesman said Britain was asking the Russian foreign ministry for information.
"We have been notified but it is not clear whether this report is about British staff," he added.
Russia this week accused Britain of running a James Bond-style spying operation in Moscow using a receiver hidden in a fake rock to gather secret information and said it had caught British spies funding pressure groups.
"Two British spies have been arrested. Of course they are not silent they are talking"
Former head of the FSB (Russian Intelligence Agency)
Four British diplomats were named as spies in a programme shown on state television last Sunday.
President Vladimir Putin, himself a former KGB spy, said on Wednesday he had not decided whether to expel the diplomats who were named.