The government's move to make information on public sector expenditure available to the public will lead to more transparency and add £6bn to the economy, Cabinet Office minister Francis Maude has claimed.
Speaking at the Wellcome Trust in London, he said the decision will boost private enterprise, "New contractors looking online will be able to see deals and say, 'We can do that for half the price'." The system will open up more government contracts to small businesses, he said.
From January, government departments will publish every month all spending over £25,000 for contracts.
In a pre-recorded message, David Cameron said public scrutiny will act as a straightjacket on spending. "This will make a difference to the deals we get and real value for money for the public. You will have so much information you won't know what to do with it. Use it. Exploit it. Hold us to account," he said.
The launch represents an important development in an international move toward open government, said Sir Tim Berners-Lee, inventor of the web. "This thing we have is a movement, it's very exciting. It will help us to accelerate the economy and create jobs," he said.
Nigel Shadbolt, professor at the University of Southampton and Berners-Lee's collaborator on opening up government data, agreed. "Open data is the basis of modern science, it goes right back to John Snow who first associated cholera with water supplies right up to the genome," he said.
"The race to the top between cities and government is going to be an extraordinary learning process."
Maude described the reforms as one of those rare moments when a government policy is absolutely irreversible and here to stay.
However, he conceded that it could create some embarrassing revelations for the government: "There will be moments - I have no doubt at all - that will be very uncomfortable."