His Championship pedigree was nothing to get excited about. He was 7th in the 1968 Olympics at altitude in Mexico and 13th in the 1972 Olympic Games in Munich. He did not fare well in the British Commonwealth Games either; he dropped out of the race at both the 1970 and 1974 Games. Clayton will mostly be remembered for his sensational, barrier breaking, world records during the 60's.

He will also be remembered for the manner in which he attained/pursued these records. In 1967 at the Fukuoka Marathon in Japan, Clayton entered the event with a personal best [PB] of 'only' 2:18:28, whereas his opponents had PB's almost 5 minutes faster. This did not deter Clayton matching the legendary New Zealander, Mike Ryan, stride for stride through the first 5km in 15:06. Ryan had always planned on going out at such a pace, however he had not banked on having his Australian neighbour alongside him. They continued this relentless pace covering 10Km in 29:57 and 15Km in 44:57. Approaching 20Km the wind turned against the runners and the immense frame of Clayton edged ahead. Clayton was alone at the 20Km split of 59:59, this first occasion the 1Hr mark was 'dipped' during a marathon. 21Km passed in 63:22 and amazingly the Japanese runner Sei-ichiro Sasaki was closing the gap on the front running Aussie.

The two were side by side by 30Km, passing through in 1:30:32. The two athletes were like the long and short of running, with Clayton at 188cm and Sasaki at 166cm. All the betting money was against the taller athlete, after all how could a man of such bulk be able to match his smaller opponent? Amazingly the two athletes began to exchange surges in the hope of testing one another. At 34Km Sasaki experienced the onset of side stitches and Clayton seized his opportunity to draw ahead. Sasaki was now a spent force and Clayton's pace began to diminish, running 16:05 for the 5Km split from 35 to 40Km. At 40Km his time read 2:02:16 and the chance of the first sub 2Hr 10 was still a distinct possibility. As history records he achieved this by establishing a new World Record of 2:09:36, bettering the previous record by almost 3 minutes, which had stood at 2:12:25. The Japanese runner, Sasaki, held on to record the 2nd fastest time in history by finishing in 2:11:17. Clayton was now on top of the world and has been recorded as saying that "this was the most memorable event of my life". Amazingly this was his 5th marathon and the first occasion that he had raced outside of Australia.

The following year, 1968, Clayton went on to finish 7th at the Olympic games with a time of 2:27:23. And because of the injuries he had begun to accumulate he was considered a spent force. He has also been quoted [in hindsight] as saying 'If I had my competitive career to run over again, I would change some of my attitudes to injuries. I would show them more respect. Because, after all, injuries weren't some unknown barrier I was trying to break through. Injuries were simply my body telling me that something wrong was happening'.

Then in 1969 Clayton appeared at the Antwerp Marathon, where he would again shock the world with yet another brutal display of front running, as well as 'ruffling a few feathers' before the event. Clayton had come to conquer all before him and wanted to put the world record 'out of sight'. His 'charming' personality did not endure to his opponents.

Take note of the conversation recorded between those who were to compete against him. Clayton was talking to the Irishman Hogan and Englishman Alder and he stated: “I’m glad you guys are here because I’m going to smash you into the ground. I think I can run a world record. I’ve just come from Ankara in Turkey where I ran 2.17 and it was a breeze and I think I can go under 2.10.” Alder said: “I don’t give a damn about world records. I would rather win the Olympic gold even if I ran 2.30. I reckon that nobody remembers who holds world records. Everybody forgets them almost as soon as they’re made.” Clayton said: “We’ll I’m going to run the world record anyway and I bet you’re wrong. People will remember my world record. You won the Commonwealth Games but they won’t remember you. They’ll remember my world record.”

On race day, the Canadian Robert Moore set off at a suicidal pace passing through 10Km in 29:25. Clayton was soon to pass Moore as he set off on his relentless solo run to achieve his objective. The objective being the establishment of a world record which would stand till 1981.

In 1970 Clayton was to race the Traralgon Harriers Marathon in Australia setting a course record of 2.13.39 which still stands today, with no athlete coming within 10 minutes of the course record since.

Unfortunately, Clayton was never to race at the high standards of the late 60's, however he will always be remembered, eventhough he was never to capture a major championship medal.