(It has been speculated by some historians that Newcastle, known to have flirted with Jacobitism, was actually contemplating a judicious "conversion" to the Stuart cause when the Prince's army reached Derby.)
It also depicts the American Revolution as not taking place because of the judicious intervention of Charles Edward, George Washington going on to become a great British general, and other flights of fantasy.
He published biographies of Lord Bolingbroke, of the early-20th-century British cabinet minister Walter Long, and of three Spanish kings: Philip II, Charles III, and Alfonso XIII.
He supported, with reservations, Spanish dictator General Francisco Franco and was a friend of a leading pro-Franco diplomat, the 17th Duke of Alba.
Along with NER editor Douglas Francis Jerrold, Petrie formed in 1937 a group concerned to put the Nationalist case on the fighting in the Spanish Civil War.