For her few scenes with Michael Caine, Shelley Winters couldn't understand his dialogue at all, due to his strong Cockney accent, and had to wait until her leading man stopped moving his lips, before responding with her lines.
On its original release, the film had an all instrumental soundtrack, by Sonny Rollins. The Oscar nominated song, by Burt Bacharach and Hal David, was added for the American release, and to a UK re-release. For the UK re-release, the song was sung by Cilla Black over the end credits, which went to number 9 on the British charts. For the U.S. release, the song was originally to be sung by Dionne Warwick over the end credits, but was replaced at the last minute, by the version sung by Cher. Ironically, Warwick's version outperformed Cher's on the Billboard charts. Burt Bacharach produced Cilla's version, although George Martin insisted his be the only name to be credited.
A rarity in film, Alfie (Michael Caine) sporadically engages the audience by looking straight into the camera as he voices his thoughts, a technique known as "breaking the fourth wall". Curiously enough, Lewis Gilbert went on to direct Pauline Collins as the title character Shirley Valentine (1989), in which she also spoke her thoughts directly to the viewer.
The power station in the background where Humphrey gives his mother's gold ring to Gilda is the Lots Road Power Station with its original four chimneys, each 275 feet tall. Opened in 1905 to supply power to the newly electrified Underground railways, it was converted from coal to oil in the 1970s and due to the lower emissions from gas the numbers of chimneys needed was reduced, so two were removed. The station stopped generating power in 2002.
As Alfie enters the Busy Bee Transport Café, the camera cuts away, and on return, a fresh advert has been placed on the background windows. This is advertising the Rolling Stones, a relatively new group on the scene, around the time the film was shot.