Gordon Brown has reaffirmed his backing for the London Olympics, promising "total support" from his government.
The initial estimate for staging the Games was £2.35bn
In a letter to International Olympic Committee (IOC) chief Jacques Rogge, he says "robust" funding is in place.
The letter, to be read out at an IOC session in Guatemala, reiterates Mr Brown's hopes the 2012 event will help inspire a "fitter" Britain.
Delegates will also hear from IOC inspector Denis Oswald, who gave London organisers a glowing report in June.
Mr Brown's letter says: "The funding for the Games is robust and provides a solid foundation upon which planning for the London 2012 games can proceed with certainty and commitment.
"I want to assure you that this government's support that has underpinned the Olympic project from the very earliest of days of the bid, through to the win in Singapore and onwards, will remain strong throughout the rest of the preparations for the Games."
The letter, to be read out by London 2012 chairman Lord Coe, continues: "This is a project like no other. Not only will it provide us with much-needed sporting and community facilities but it will also help regenerate some of the poorest areas of the United Kingdom."
It follows controversy over the cost of the games, which has risen from £2.35bn to £9.35bn.
An extra £675m of lottery funds has been allocated to help fund the project. Olympics minister Tessa Jowell has said sales of the 312 hectares of Olympic Park land in Stratford, east London, will help pay that back after 2012.
Over the period 2006 to 2012 about £1 in every £5 of lottery money spent on good causes is going towards the Olympics.