Iran’s release on Wednesday of footage of the 15 British sailors and marines detained on Friday was designed both to show that they were healthy but also, perhaps, to demonstrate that Tehran believes it retains the upper hand in the six-day old affair.

In her interview, Faye Turney, the only woman among the 15, described her captors as “hospitable” and in her letter to her family, screened in the footage, wrote that she and her colleagues had “three meals a day and a constant supply of fluids”.