[1] Together with his two brothers, also professional musicians, he played in the band run by his mother until serving in the Royal Air Force.
[1] In 1953, Hamer moved to London to work for clarinettist Carl Barriteau and a brief period with the Oscar Rabin Band.
[3] Hamer also played in big bands led by Tubby Hayes, Ted Heath, Mike Gibbs, Jack Parnell and Harry South.
He also played with Kenny Wheeler, Dizzy Gillespie, Ella Fitzgerald, as well as smaller bands with Stan Tracey, Benny Golson, Lalo Schifrin, Gary McFarland, Woody Herman's Anglo-American Herd, Barbara Thompson, the Thad Jones-Mel Lewis band, Eric Delaney, John Dankworth and Joe Harriott.
As a session musician, he played on recordings by The Beatles ("Got to Get You into My Life" ) and Bing Crosby, Tom Jones, Dusty Springfield, Shirley Bassey, Barbra Streisand, James Last, Matt Monro, and Peter Herbolzheimer.