An espionage saga that involved a well-liked teacher of US diplomats, the illicit use of shopping carts and a much publicised denunciation of the US-UK special relationship took a new turn on Friday when the US state department accused a former employee of working as a Cuban spy for almost 30 years.

The indictment of Walter Kendall Myers, who was given “top secret” security clearance in 1985 and went on to work part-time for the department’s Bureau of Intelligence and Research from 1988 and full time from 2001, followed a three-year investigation by the FBI and the department.