The only film from British sex-film era (1958-1984) which was a big hit in America, as well as the UK. Producer Stanley Long claimed it netted him £1m (approximately £15m as of 2023).
Originally titled The Wife Swappers.
Norman J. Warren was originally offered the job of directing, but after making a couple of sex films, he wanted to get away from that type of film so he wouldn't be typecast. But it took several years to find work again. He was finally hired to direct the horror movie Satan's Slave (1976).