Sewell won the Brabazon Trophy at Moortown Golf Club in 1957, finishing 8 strokes ahead of Tony Slark.

[2] The following year he won the English Amateur at Walton Heath Golf Club beating the Rhodesian David Proctor 8&7 in the final.

[3] He came close to winning the Berkshire Trophy in April 1959, finishing a stroke behind Joe Carr after making a bogey at the final hole.

[5] He won the English Amateur for the second time in 1960 beating Martin Christmas in the final on the 41st hole at Hunstanton Golf Club.

Sewell's only important professional win was in the 1970 Martini International at Conwy Golf Club where he tied with Peter Thomson.