Coslett had 15 seasons at St Helens up till 1976. He was a brilliant goalkicker landing 1,639 career goals and scoring 45 tries for the club. He started as a tough-tackling, raw-boned youngster. A broken ankle later in his career cost his blistering pace, but he remained ever a dangerous player with the ball in hand.
Coslett ended up a utility player, playing in every position from full-back to loose-forward for St Helens. After the 1972 Challenge Cup final he was awarded the Lance Todd Trophy for his man-of-the-match performance.
Coslett went on to coach Wigan and Rochdale Hornets and remains involved at the St Helens club 44 years after first signing.