The government has been accused of sitting on almost £2.5bn-worth of assets that have been earmarked for good causes and charities, many of which face an uncertain future as funding streams start to dry up.

Some of the money – due to be recouped from the sale of Olympic assets built with national lottery money that was originally earmarked for good causes – will not be repaid for 30 years or more, it is being claimed. The government has also declined to say what it intends to do with the lion’s share of the assets, currently sitting in dormant bank accounts, share portfolios and bond holdings.

In March, the Dormant Assets Commission said in its final report that it had identified some £2bn of unclaimed cash that could be freed up and distributed to good causes. The commission said the “huge sum has the potential to further transform the charity sector, helping to improve communities and change lives”.

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At the time the minister for civil society, Rob Wilson, said: “This money could help change millions of lives across the country by helping good causes rather than gathering dust in dormant accounts.” But now, almost a year on, the government is still considering the commission’s report and has yet to publish its response.

Labour MP Steve Reed, the shadow minister for civil society, said: “The commission identified £2bn that had been locked up; it’s unclear who owns it and it’s not been touched for many years. They said it could be used but the government have never used it.”

In 2010, the coalition government also promised to make good on a Labour government pledge to repay £425m taken from the Big Lottery Fund to pay for the 2012 Olympics. Most of the money was for grants of less than £10,000 which were intended for grassroots projects across the UK.

Jay Kennedy, director of policy and research at the Directory of Social Change, which provides advice and support to the charitable sector, said an immediate refund of the £425m owed to the Big Lottery Fund could help millions of people across the UK by supporting vital projects and services. “It would support at least 42,000 mostly local, grassroots charities and community groups,” Kennedy said. “Critical services for people in need – such as children’s hospices in Scotland, food banks in Wales or activities for isolated older people in the north east.”

The government had said that it would repay the money by selling off Olympics assets by the early to mid-2020s but it has now emerged that only £57.5m has been generated so far and none has been handed to good causes.

“You can’t help but think the government isn’t focusing,” Reed said. “In government speak, the mid-2020s is 10 years’ time. At the rate they’re currently planning to repay, it would take a further 30 to 40 years to get the money back to people. That’s way too long.”

One of the biggest assets, the Olympic stadium, has been signed over to West Ham football club, which is paying £2.5m a year rent on its 99-year lease.

The need to free up the cash for charities is likely to increase post-Brexit. Currently, some £250m a year of EU funding goes to the UK voluntary sector. “But the government has given no answers on how that funding will be replaced,” Reed said. “Charities are in a tough position and it’s going to get even tougher, and yet the government has a means to support them.”

Kennedy said charities were facing funding cuts while demand for their services was rising. “Lottery revenues are declining too, which also threatens the pipeline of future grant support,” Kennedy said. “That’s why we need a Big Lottery refund now.”

A spokeswoman for the Department for Digital, Culture, Media and Sport said: “We have always been clear how money that helped fund the 2012 Olympic and Paralympic Games will be returned, with the £425m the Big Lottery Fund contributed to be repaid from the early 2020s. We are to publish our response to the Dormant Assets Commission report soon.”