This is the film that Sean Connery made while taking a break from Bond movies. Due in part to the difficult time Connery had in Japan while filming You Only Live Twice (1967) the Bond producers released Connery from his contract (otherwise he would have been required to star in On Her Majesty's Secret Service (1969)).
According to her memoirs Ingrid Pitt was considered for the role of Lady Julia but turned it down to pursue a (successful) casting role in Where Eagles Dare (1968).