Steve Cram won a silver medal at the 1984 Olympics

He told the Labour Party conference on Monday the city was in with a "winning chance" of hosting the Olympics.

The success of the Commonwealth Games in Manchester had shown what a major sporting event can do for an area and a country, he said.

And bringing the Games to London would raise the profile of British sport and bring benefits to London and the rest of the UK.

"We've all got to get behind it," he told conference delegates.

"We've got to stop being a nation that thinks we can't do things, particularly in the world of sport, there's too much doom and gloom around."

The biggest winner of all will be sport in the UK Steve Cram

Cram, who was the world's leading 1500m runner in the mid-1980s, said investing in sport had knock-on benefits for health and reducing crime.

Changes brought to Athens - which is hosting the 2004 Olympics - had been "absolutely immense", the conference was told.

And a London Olympics would bring an estimated 9,000 new jobs, 4,000 homes and transport improvements.

"The biggest winner of all will be sport in the UK," said Cram.

"We need to invest in sport from the grassroots up and by doing so we will ensure we have more athletes on the roster.

"No country in recent times has hosted the Olympic Games and not had a surge in their medal performance and Britain will be no different."

London's rivals for the 2012 bid are New York, Paris, Madrid, Moscow, Leipzig, Istanbul, Rio de Janeiro and Havana.

Initially sceptical

The International Olympic Committee will decide on the host in July 2005.

Culture Media and Sport Secretary Tessa Jowell said bidding for the Olympics would "showcase Britain as a can-do nation".

She told the conference the bid process was "really moving", and said: "This will be a bid to rival the best. And we are backing it 100%."

Gateshead-born Cram admitted he was initially sceptical about the London bid.

But he added: "With all the support that's now been gathered behind the bid I really now believe London has a winning chance in this race."