In 1970, Richard Lester had planned to make a movie of "Flashman", the first of George MacDonald Fraser's novels, from a screenplay by Charles Wood and Frank Muir, with John Alderton in the title role. Because of the expense, it was canceled days before shooting was scheduled to start. Four years later, after collaborating with Fraser on his two "Musketeers" movies with huge success, Lester tried to reactivate the project. He found it easier to make a movie of Fraser's second novel, "Royal Flash", perhaps because the story is a parody of "The Prisoner Of Zenda", which had been filmed several times before. United Artists went cold on the idea shortly before filming was set to begin, but Lester was able to successfully transfer the project to Twentieth Century Fox. The movie was a critical and box-office failure, and for general release in Britain it was cut from one hour fifty-eight minutes to one hour thirty-six minutes. George MacDonald Fraser hated the film so much that he would refused to authorize any more films based on his Flashman novels in his lifetime.
When the film was cut from 1:58 to 1:36, it 20 actors' performances were removed, including Roy Kinnear.
In the throne room, just after the wedding, the U.S. Ambassador is introduced as Cassius Clay. That is the birth name of boxer Muhammad Ali who defeated boxer Henry Cooper. Muhammad Ali was named Cassius Clay at birth, after his father, who was named after a famous 19th century Kentucky politician and anti-slavery activist, who President Abraham Lincoln later named Ambassador to Russia.
When Henry Cooper and Oliver Reed were supposed to spar, Reed started throwing real punches at Cooper. Cooper eventually became annoyed and threw a punch so fast that nobody saw it land. Reed hit the floor, eventually got to his feet, and said in a German accent, "Thank you for the instruction!"
The script is based on the second novel in the Harry Flashman series, better known as "The Flashman Papers".