What was wrong with this typically British idea....
"Lord Mountbatten faced the problem of what to do in the event of a four-minute warning if Harold Macmillan was away from his desk...The Treasury didn’t want to spend any money; Macmillan didn’t want to have any fuss at all. .....Whitehall arranged for the prime minister’s car to have a radio link – with which the AA used to communicate with its mechanics – that would tell the PM's driver that he needed to reach a public phone box, from which Macmillan would call Whitehall. It was suggested that government drivers carried four pennies, as that was the minimum sum needed in a GPO phone box.”
Can't see all the above being done in four minutes...