David Cameron said a new £600 million Big Society fund would be used to help tackle the country's "deepest social problems".
The Prime Minister claimed the money would help "smash away" the "patronising assumption" that small charities cannot do big things.
The initial capital for the fund will be an estimated £400 million in unclaimed cash from bank accounts dormant for more than 15 years and £200 million from Barclays, Lloyds, HSBC and RBS.
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His representatives said Cassidy, who was hospitalised last week, died "surrounded by those he loved."
The company’s recently appointed Chief Executive Dara Khosrowshahi said the breach was made by two individuals outside the company.