Usain Bolt begins the defence of his 100 metres title at the London Games today, as Michael Phelps has one last chance to add to the biggest Olympic medal haul of all time.
Bolt, the charismatic Jamaican who lit up the 2008 Beijing Games with three golds and his trademark lightning bolt celebration, will run in the heats of the shorter sprint, the most anticipated event of the Games.
Also limbering up for Sunday's final will be the three other fastest men in history, all intent on toppling him: fellow-Jamaicans Yohan Blake and Asafa Powell, and Tyson Gay of the United States.
The last night of swimming action will see Phelps join his American team mates in the 4x100 metres medley final and looking for his 22nd Olympic medal.
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After a showery start to the day, parts of Northern Ireland, western Scotland and south-west England will see drier conditions.