Glen started playing harmonica after seeing Muddy Waters, and the 'American Folk-Blues Festivals' which visited London in the late 1960s and early 1970s.

Early bands he was involved with were Crowjane Bluesband, The Radical Sheiks and Brothers Grimm, before going on to join Nine Below Zero (1991–1995), and The Yardbirds[1](1996–2003 and 2008–2009).

In addition he appeared alongside Alan Barnes, Jim Mullen and Roger Cotton on the With Friends Like These album for the Barcodes, which also included Zoot Money.

Other collaborators include Art Themen, Pee Wee Ellis, Dub Syndicate, Paul Cox, Archive (band), Alan Barnes, Little Axe and Gypie Mayo.

Glen has played at Montreux, Brecon Jazz Festival and Nice Jazz Festivals, Hollywood House of Blues, the Hilton, Las Vegas, Sporting Lisbon Stadium, Wembley Arena, Ronnie Scott's Club and The Royal Albert Hall, as well as various television and radio performances.