"I Won't Let You Down" is a 1982 single by British band Ph.D. It entered the UK charts in April 1982 at #34 and peaked at #3 in May of that year. The band consisted of Jim Diamond who was the lead vocalist, Tony Hymas on keyboards and Simon Phillips on drums. It went on to become the 23rd best-selling single of 1982 in the UK.

The album and 7" single versions (which is usually the version played on radio) of the song are subtly different – the single version begins with a synth-based introduction based on the song's main hook, whilst the album version goes straight into the first verse. The album version also has one additional repeat of the "I won't let you down" line in the second rendition of the chorus, and has an additional drum fill in during the repeat of the chorus on the second verse. The music video of the song uses the album cut, whilst many 1980s compilation albums use the single cut instead.

There are two video versions of this song.

The original video of the song was set in and around the Queensway area of West London. As with the band's previous single "Little Suzi's On The Up", the video is shot in a slapstick comedy style and features Jim Diamond as a well-dressed man trying to win back the affections of his lover (thus mirroring the theme of the song) using presents and taking her to upmarket bars and restaurants. Tony Hymas appears as the video’s antagonist; in various scenes dressed in various disguises he makes unsuccessful attempts to assassinate, or maim Jim Diamond’s character in order to win the affections of the woman. He is finally successful when, posing as a car dealer, he lures Diamond into a second hand car (a white Fiat 128), which is revealed to be on the end of a crane in a scrapyard being lifted up, whilst Hymas walks away with the girl as the camera zooms out and fades to black.

The second version was set in a dressing room at a club with Diamond performing the song as he professes his love to a woman sitting next to him. He also looks at the mirror and after he turns around his image also sings. In the end, Diamond does win over the woman, but after he leaves the room as his mirror image walks up to her (who was in actuality looking in the mirror at Diamond).

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