Glascock died at the age of 28 as a result of a congenital heart valve defect, which was worsened by an infection caused by an abscessed tooth.

He played with The Gods (early 1965 – June 1967, September 1967 – February 1969) where, together with future Uriah Heep members Ken Hensley and Lee Kerslake, he recorded the album Genesis.

After briefly playing with Head Machine (1970), he joined Toe Fat (June 1969 – December 1970), working with Hensley and Kerslake.

Unlike his later work in Jethro Tull, in Carmen he used effects, such as a fuzz pedal in the song "Viva Mi Sevilla".

Glascock's health problems became apparent when he was unable to complete the 1979 US leg of the Heavy Horses tour, missing a transatlantic simulcast from Madison Square Garden.

He learned of Glascock's death in November 1979 during the US Stormwatch tour, with replacement bass player Dave Pegg, and had to break the news to the rest of the band.

Glascock's touring replacement on bass, Dave Pegg, was retained for the band's follow-up album in 1980 and remained with the group until 1995.