Jim Diamond (born 28 September 1953, Glasgow) is a Scottish singer-songwriter. Diamond is best known for his three Top 5 hits. The first was "I Won't Let You Down" (1982), as the lead singer in the trio Ph.D., with Tony Hymas and Simon Phillips. His solo performance, "I Should Have Known Better", was a United Kingdom number one in 1984. The third track was the theme song from Boon, "Hi Ho Silver" which reached Number 5 in the UK Singles Chart in 1986.