The title derives from the tradition that Victorian/Edwardian pharmacists (such as Edward Sutton) would dispense all drugs in a package sealed up with pink string and sealing wax; doing this would prove that the product had not been adulterated on its way to the customer.
The film is set in the English seaside town of Brighton in the 1880s. (Madame Adelina Patti's poster for her impending performance at the Brighton Pavilion gives a date of [Friday] May 7th 1880.)
When submitted to the US Production Code Administration in script form in November 1947, it was rejected because it showed details of a crime and ended with a suicide. It was released without receiving a PCA Seal of Approval.
The film premiered in London, (on 3rd December, 1945), at the Tivoli Cinema on The Strand, and the Marble Arch Pavilion. The critic in The Times praised Googie Withers and Gordon Jackson for their roles, and concluded that Robert Hamer, "has made, in spite of occasional lapses and longueurs, a promising beginning as a director."
Though it was Jean Ireland who played the older sister with singing career aspirations, in real life it would be Sally Ann Howes, playing the younger sister, who would go on to have a huge success on stage as a musical performer.