Clayton played for Lancashire's second eleven in 1956 and 1957, but made his first-class cricket debut in the 1957 for the Combined Services cricket team while on national service.[4] On discharge, he returned to Lancashire and was brought into the first team at the start of June 1959, remaining then as first-choice wicketkeeper until he left the county at the end of the 1964 season. In his first innings for the county side, he top-scored with 43.[5] In his third County Championship match, against Middlesex at Liverpool, he scored an unbeaten 74.[6] The batting was a bonus: Lancashire's previous first-choice wicketkeeper, Alan Wilson, had a career batting average of less than six runs per innings.[7] But Clayton in his first full season averaged more than 24, and though he did not sustain this, and the 74* remained his highest score until 1963, he batted for most of his career at No 7 or No 8.[8] Clayton's arrival was noted by Wisden Cricketers' Almanack's 1960 edition: "In the sturdily built Clayton, Lancashire discovered a wicketkeeper of real promise and lively character," it wrote.[9]
Clayton was awarded his county cap in 1960, when he made 89 dismissals – his 76 catches for the county were a Lancashire record.[10] It could have been more, but he was dropped for the final three matches of the season, and Wisden in 1961 mentioned this as part of a short list of "perplexing" events indicating disharmony at Lancashire.[11] Unlike Jack Dyson, who was sacked, and Alan Wharton, who moved to Leicestershire, Clayton was back for a full season in 1961, playing in 37 first-class matches in the season, though this was one of his less successful seasons as wicketkeeper. He was back to form in 1962 and with 92 dismissals, this was his best season in first-class cricket.[8] The 86 catches for Lancashire that season remain the county record.[10]
The 1963 season proved to be Clayton's best with the bat: he scored 894 runs in all matches at an average of 22.92.[8] And, sent in as a nightwatchman in the match against Sussex at Hove he made 84, the highest score of his Lancashire career.[12] But the following season, 1964, the discord at Lancashire resurfaced and at the end of the season Clayton was not re-engaged. The club issued a statement: "The committee have reviewed the performance of the team both on and off the field during the current season in conjunction with a special report which had been called for. A firm decision was taken not to re-engage P. Marner and G. Clayton on the grounds that their retention was not in the best interests of the playing staff or the club."[13] During the 1964 Gillette cup tie against Warwickshire, in protest at the opposition's ultra defensive field placements he decided to block out, eking out 19 runs in 20 overs and leaving Lancashire well short of the target. There were protests from Lancashire supporters, described as a minor riot when they gathered in front of the pavilion calling for Clayton's head.[14]
Dyson, who had returned after being sacked in 1960, was also not re-engaged, and Ken Grieves was replaced as captain. Though much of the county committee was then replaced in the end of year election, Clayton was not reinstated and had in any case by then joined Somerset.