James Aaron Diamond was a Scottish singer-songwriter, best known for his three top 5 hits: "I Won't Let You Down" (1982), as the lead singer of PhD; and his solo performances "I Should Have Known Better", a United Kingdom No. 1 in 1984, and "Hi Ho Silver", the theme song from Boon, which reached No. 5 on the UK Singles Chart in 1986.

"I Won't Let You Down" is a song by British band Ph.D., released as the second single from their eponymous debut studio album (1981). It entered the Australian charts in October 1981 and reached number five; it entered the UK Singles Chart in April 1982 at number 34, peaked at number three the following month. It went on to become the 23rd best-selling single of 1982 in the UK.