Some 700,000 savers are thought to have missed the boat for reporting endowment mis-selling complaints.
This means that close to 10% of borrowers facing shortfalls on their endowments are now cut adrift from any recourse.
The Treasury revealed the figures in a submission to the Commons Treasury Select Committee which is looking into the crisis.
The Consumers' Association has slammed the revelation as a sign of both the Financial Services Authority's and the industry's complacent handling of the endowment problem.
Teresa Fritz, principal researcher at the Consumers' Association, says: “The public needs to know when the Treasury and the FSA knew about the sheer number of consumers who might be denied redress.
“As a first step the CA is urging companies to follow Legal & General's lead in waiving the right to impose time-bars for people who have been mis-sold endowment mortgages.
“As for those who refuse, the CA is calling on the government and the FSA to force the Association of British Insurers and the rest of the insurance industry to guarantee consumers who are entitled to compensation the redress they deserve.
“We will regularly publish a statement of the companies prepared to waive time-bars on customers entitled to redress – and those that refuse.”
The government says that once it has a clearer picture of the numbers involved it will be looking to resolve the problem in conjunction with the FSA.