Reddish had been a keen swimmer as a youth, and when his sight deteriorated he decided to become classified as a disability swimmer. Initially classed as a B2 athlete with reduced vision, he entered his first international tournament, the European Championships in Switzerland, in 1989. There he won 11 medals, including two gold. Reddish first represented Great Britain at a Summer Paralympics at Barcelona in 1992. In Spain Reddish won two medals, a silver in the 100m butterfly B1-B2 and a bronze in the 100m freestyle. Four years later he competed at the 1996 Summer Paralympics in Atlanta. Competing in five events, and now swimming as a B1 athlete (completely blind), he matched his achievements from Barcelona with another silver and bronze, this time in the 200m medley and the 100m freestyle. His final Paralympics as a competitor were the 2000 Games in Sydney. There he collected his fifth and final medal, winning silver in the men's 4 × 100 m Medley for S11-13 category swimmers.