"The VC10 was used for the Queen's bicentennial tour of America. On July 3, 1976, the Queen and the Duke of Edinburgh embarked on a tour of the USA with the first stop in Bermuda."
True enough - and once HM had embarked at Heathrow, the crew requested Start and ATC clearances, when it emerged that BA Ops had failed to file the Flight Plan submitted. The Captain then gently but very firmly insisted that there was now no question of a delayed departure, and that he would start and taxi towards the runway in use for takeoff, by which time he expected a departure clearance of some kind to be available. He did, and one was - and an apology from somebody very senior in BA was subsequently received at MOD(Air).