A Treasury report published last week said the fund should administer a scheme to spend dormant funds on a range of services for young people.
But members of the Commission on Unclaimed Assets told Third Sector that Gordon Brown had privately endorsed a social investment bank and they hoped both ideas would go ahead.
"We have had contact with the Treasury and the Chancellor and they are very supportive that we continue to proceed with the ideas put forward in our report," said Geraldine Peacock, former chair of the Charity Commission and a member of the CUA. "Our resolve is to make the bank happen one way or another."
George Mudie, Labour MP for Leeds East and a member of the House of Commons Treasury Committee, which is currently examining unclaimed assets, said in an evidence session two days before the launch of the Treasury report that the Big Lottery Fund did not reach deprived communities effectively.
Stephen Bubb, head of chief executives body Acevo, said that any unclaimed assets going to the fund should be administered separately from the fund's other revenue.
"The money for youth projects must be operated transparently and must not be seen as additional to the lottery's own funds," he said.