The Directory of Social Change has called for any Olympic underspend to be sent straight back to the Big Lottery Fund, after the Department for Culture, Media and Sport announced that the games were likely to come in almost half a billion pounds under budget.
A DCMS statement said £476m of contingency funds remained in the Olympic budget thanks to savings made by the Olympic Delivery Authority. In 2007 £675m was diverted from lottery good causes income to support the games, including £425m from the Big Lottery Fund.
"With only 44 days to go before the Olympics, it is fantastic news that there is still £476m of contingency funds left," said Jeremy Hunt, the culture secretary.
The overall funding package for the games stands at just under £9.3bn, with £476m of uncommitted contingency funds available, the statement said.
Jay Kennedy, head of policy at the DSC, said that the money should go straight to the Big Lottery Fund. The training and publishing charity has been spearheading a campaign for the government to reimburse the fund as soon as possible.
"It will be an utter outrage – and verging on money laundering – if lottery revenues raided by the government to fund the Olympics go back to the Treasury," he said.
"This money was taken away from supporting vulnerable people and communities across this country at a time when they needed it most. Government needs to keep its promises and do the right thing – any underspend must be used to refund the lottery as soon as possible."
A DCMS spokeswoman said the funds would be repaid from the resale of land from the Olympic Park after the games.
But John Penrose, the minister for tourism and heritage, said in February that money from land sales was unlikely to begin to return to distributors until the mid 2020s.
The DCMS spokeswoman said: "The amount we have announced today is not a fait accompli. That money is still available to be used as contingency and will not go back until after the games. We believe, however, that we are on course for an underspend."