Tommie Smith was the first athlete to run the 200 metres inside 20 seconds, but he'll always be remembered instead for his clenched-fist black power salute on the medal podium at the 1968 Olympics.

Smith and fellow black American runner John Carlos wore black gloves and raised their fists during the medal ceremony at the Mexico City Games in a protest that electrified the world and became an iconic image for the civil rights movement.

Over 40 years later, Smith is in London ahead of this year's Olympics where he attended the first British showing Wednesday of a film that documents the protest.

"Salute" shows how gold medal winner Smith, Carlos and the third man on the podium that day, Australian Peter Norman, were shunned by their countries for the defiant statement. Silver medallist Norman wore a human rights badge on the podium in support of the American pair and also was ostracised by the sporting establishment in his home country. He died in 2006.

Smith and Carlos were expelled from the Games under pressure from Olympic officials and despite Smith breaking the world record that day by running 19.83 seconds, his career in track slid away and he went on to play in the NFL. Both men suffered abuse at home and had threats against their lives.

The film that tells their story was written, directed and produced by the late Norman's nephew, Matt Norman, and originally released in 2008—the 40th anniversary of one of the Olympics' most memorable moments.

At the London premier of "Salute" Wednesday and just over two weeks ahead of the start of the 2012 Games, Smith said he thought current 200 world record holder Usain Bolt of Jamaica could break the 19-second barrier in the event. Bolt set his world record of 19.19 seconds in Berlin in 2009.