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London 2012 medals unveiled as Olympics countdown begins

27 July 2011 Last updated at 19:49 BST

The Princess Royal has unveiled the London 2012 gold medals as the one-year countdown to the Olympics began.

The medals depict the Greek goddess of victory, Nike, stepping out of the depiction of the Parthenon to arrive in the host city.

Thousands gathered in Trafalgar Square where David Cameron promised London's would be the "greatest games".