With a background in big band music, Seamen played and recorded in a wide range of musical contexts with virtually every key figure of 1950s and 1960s British jazz. Notable examples included Joe Harriott, Tubby Hayes, Stan Tracey, Ronnie Scott, Dick Morrissey, Harold McNair, Don Rendell, Victor Feldman, Dizzy Reece, Tony Coe, Tony Lee, and George Chisholm, among others. Later in his career he worked with Alexis Korner and Georgie Fame, and had a spell with Ginger Baker’s Air Force, the leader of the band being Seamen’s foremost disciple. Addiction to alcohol and other drugs hampered his career.
Seamen began playing drums at the age of six, turning professional at the age of 18 by joining Nat Gonella and his Georgians in 1944. He joined the Tommy Sampson Orchestra in 1948, and by 1949, Seamen and tenor saxist Danny Moss had formed a bebop quintet from within the ranks and which was featured on a radio broadcast by the orchestra in September 1949.