"We can't muddle through greening our economy. We need investment, planning and an Olympic-style national crusade," Brendan Barber, general secretary of the Trades Union Congress, told the organisation's annual conference near London.

"We won't build up industrial strength unless we work out what we do best as a country, whether it's cars, pharmaceuticals, aerospace or the creative industries, and help them do even better.

"And just as the Olympics needed new infrastructure, so does the rest of the country."

Barber added in a speech made in the Brighton coastal resort: "Britain is at a historically important crossroads. The choice we face is clear. In one direction is decline, depression and despair. In the other is recovery, regeneration and renewal."

His speech came as Britain bid a fond farewell Monday to a golden summer of Olympic and Paralympic sport with a victory parade by athletes through London ending up at Buckingham Palace.

Tens of thousands of people were expected to line the streets through the centre of the capital, including the army of volunteers who worked on the Games, to cheer on Britain's medal-winning heroes.

Prime Minister David Cameron, surrounded by volunteers in their purple and orange shirts, said Monday it had been a golden summer for Britain, with the Games following celebrations for Queen Elizabeth II's diamond jubilee.

"For countries to succeed in this competitive and difficult world, you need to have confidence that you can do big things and get them right... that you can take on the best, be the best, beat the best," Cameron said.

"We've absolutely done that as a country."

Cameron's boast comes as Britain's economy is struggling to exit a deep recession.