[2] A founder member of Kelly College Swim Squad in Tavistock (along with Sharron Davies) Jameson represented Great Britain at the 1984 Summer Olympics in Los Angeles, where he finished 5th place in the 100-metre butterfly.

He then won silver in the 100-metre butterfly at the 1985 European Championships (Sofia), behind the German star swimmer Michael Gross.

Jameson took bronze in the 100-metre butterfly at the 1986 World Championships (Madrid), and then went on to take gold when representing England in the same event at the Edinburgh Commonwealth Games later that year.

He qualified fastest into the final, where he took bronze in a time of 53.30 seconds, breaking both the British and Commonwealth records in the process.

His older sister Helen was also a competitive swimmer, and represented Britain at the 1980 Olympic Games in Moscow and won a silver medal in the 4×100-metre medley relay.