Clarke was in fourth place in the 110 m hurdles at the 2008 Commonwealth Youth Games in Pune, India. He was also the British University champion in the 60 m hurdles with a time of 7.83 seconds and 110 m Champion in a time of 13.85 seconds. Clarke held the No. 1 spot on the British All Time list for the Under 20 men's 3"3 110 m Hurdles until 23 May 2010. He established a new National Junior Record with a personal best of 13.37 seconds whilst also winning gold at European Junior Athletics Championships in July 2009, in Novi Sad, Serbia.
Senior athletics career
In June 2010, Clarke won the UK National Under-23 Title in a wind-assisted time of 13.60secs. He successfully defended this title in June 2011 in his season debut that year. On 8 October 2010, Clarke won the bronze medal at the XIX Commonwealth Games in New Delhi. He finished third behind two other English hurdlers: Andy Turner and William Sharman. It is the first time in history that England have completed a 1-2-3 clean sweep in the 110 m hurdles. Clarke became national champion when he won the UK Senior 110 m hurdles title in 13.58s in July 2011, earning him a place on the UK team at the World Championships in Daegu. He competed at the 2011 World Athletics Championships in Daegu, South Korea where he went out in the first round with a time of 13.65s. The winner of his heat was Jason Richardson who went on to win the Championships after Dayron Robles, the 2008 Olympic Champion and World Record holder, was disqualified after the final.
2012 Summer Olympics
On 24 June 2012, he achieved selection for Great Britain in the XXX Olympiad in London 2012. He ran a new personal best of 13.31 in his Olympic Semi final on 8 August. As a result, he qualified as the only European for the 110 m Men's Hurdles Final as a fastest loser. Running from lane 2 in the final he finished an unexpected 4th place with a time of 13.39 seconds beating the 2009 World Champion, Ryan Brathwaite, into 5th.
Post London
He broke his wrist in the winter of 2012 followed by a series of hamstring tears that saw him miss high level competition in 2013. He returned to International competition in 2014 finishing 8th at the Glasgow Commonwealth Games. Two weeks later he competed at the European Athletics Championships in Zurich only to tear his hamstring five minutes before the call room for the European Final. In March 2015 he was appointed Team Captain of Great Britain at the European Athletics Indoor Championships in Prague. He finished 5th in the 60 m hurdles. That summer he competed at the IAAF World Athletics Championships in the Bird’s Nest Stadium in Beijing exiting in the semi-finals. After the World Championships he made the decision to leave Malcolm Arnold OBE and Bath and moved to Paris to train with Giscard Samba Koundys and Dimitri Bascou. He competed at the IAAF World Indoor Championships in Portland, USA in March 2016 just missing out on the Men’s 60 m Hurdles final. His training partner Dimitri Bascou went on to win the Bronze medal. In July 2016 he was selected to represent Great Britain at the 2016 Summer Olympics in Rio de Janeiro, Brazil. He finished 11th, missing out on the final by 0.05 of a second.