Section eight of the deal reached by Donald Trump’s former national security adviser in the inquiry into Russian meddling in the US election is entitled “cooperation”. It specifies that as well as answering questions and submitting to government-administered polygraph tests, Flynn’s cooperation “may include … participating in covert law enforcement activities”.

Long-time students of federal law enforcement practices agreed, speaking anonymously, that “covert law enforcement activities” likely refers to the possibility of wearing a concealed wire or recording telephone conversations with other potential suspects. It is not known whether Flynn has worn a wire at any time.

“If the other subjects of investigation have had any conversations with Flynn during the last few months, that phrase must have all of them shaking in their boots,” said John Flannery, a former federal prosecutor in the southern district of New York.