Christine Ohuruogu has completed one of the most sensational comebacks in sporting history by winning the women's 400 metres final at the Olympic Games.

The 24-year old from Stratford, East London, was allowed to compete in Beijing only after a British Olympic Association rule banning athletes who have failed strict drug-related guidelines was overturned in the High Court.

Ohuruogu missed three out-of-competition tests and incurred an automatic lifetime ban from the Games, and even when the ruling was rescinded many commentators criticised her attendance.

Today she has had the last word - and then some. After allowing Sanya Richards and Shericka Williams, of the US and Jamaica, to set the early pace, she kicked spectacularly at the final turn and edged past her rivals in the final few metres, coming home in 49.62 seconds. Richards, the pre-race favourite, got her tactics badly wrong and looked leaden-footed in the home straight as she trailed in third.

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"As I crossed the line I was thinking 'Oh my gosh, I think I've won,'" said Ohuruogu. "I thought it was just a dream and now it's become a reality.

"I am just so proud of myself. I know I can perform when I need to. I may not have a good season but, like at the World Championships, that's what I train all year for."

Ohuruogu returned from her ban with an against-the-odds victory in the World Championships in Japan last year. Richards missed that race after failing to qualify and many suspected the 23-year-old American would be too good today, but she blamed her bronze medal on a mid-race injury.

"I'm not well. I worked so hard for this and it is so devastating for me," she said. "The gold would have been mine if it weren't for a hamstring grab.

"I was in control for half of the race - by the 320m mark I felt my right hamstring. I pulled my leg through and it got tighter and tighter."

Second-placed Williams admitted she failed to recognise the threat posed by Ohuruogu.

"I was thinking too much about passing Sanya and didn't give Christine too much focus," she said.

It is the fourth gold medal of the day for Great Britain - and 16th overall - in what has become the most successful Olympic Games for the country since 1908.

In the velodrome, Chris Hoy made Olympic history by becoming the first British athlete in a century to clinch three golds at one Games.

The powerful 32-year-old achieved his feat by beating his team-mate Jason Kenny 2-0 in the final of the men's individual cycling sprint, reaching speeds in excess of 70kph as the two riders threw themselves into a high-octane battle.

Hoy's achievement followed that of fellow cyclist Victoria Pendleton, 27, who won the three-legged women's individual sprint shortly beforehand, and Paul Goodison, who won Britain's third sailing gold in the Laser class.

Goodison just missed out on a medal at Athens four years ago, triumphed in conditions so windy he had described them as a "lottery". "I just can’t wait to go and find my mum and give her a big hug after all the heartbreak I gave her in Athens," he said.

The athletics team also picked up an unexpected silver medal in the high jump when the little-fancied Germaine Mason leapt 2.34 metres to equal his personal best.