Presbyterian Mutual Society was placed in administration in November
The Prime Minister will not consider helping investors in the Presbyterian Mutual Society until he sees a report investigating its problems.
Nearly 10,000 savers were hit by the collapse of the society.
The First Minister Peter Robinson told the assembly he discussed the matter with Gordon Brown earlier this month.
Mr Brown was told the government had some responsibility because the run on the PMS followed government moves to prop up the banks.
Members of the society voted overwhelmingly in February to allow the administrator to run down the company in an orderly manner over time.
Investors voted on five resolutions allowing the administrator to prepare proposals for the society's future.
They were all passed by a majority of around 90%.
The society was put into administration last November.
In January, the administrator, Arthur Boyd, wrote to 9,500 investors recommending that they accept a proposal, which he said would give them some of their money back.