Having played for Liverpool RFC, Colclough went on to become one of the first Englishmen to play in France; he ended up captaining Angoulême, and also later played for Wasps RFC and Swansea RFC. He made his international debut on 4 March 1978 at Murrayfield in the Scotland vs England match, and his final match for England on 15 March 1986 at Parc des Princes in the France versus England match. Of the 33 matches he played for England, he was on the winning side on 17 occasions. Colclough was a member of the England team that won the Grand Slam in 1980. He was selected for the 1980 British Lions tour to South Africa and the 1983 British Lions tour to New Zealand, playing in all four internationals each tour. In 1983, he scored a try for England against New Zealand at Twickenham.