Britons may have to work longer or save more to pay for the UK's £57bn pensions shortfall, an independent government report is expected to warn on Tuesday.
Britons are reportedly putting only £40 billion into private pensions
The Pensions Commission's estimated figure - leaked to the Sunday Times - is nearly double previous forecasts.
Pensions Secretary Alan Johnson has warned that the Commission's findings will present "stark choices", but has ruled out tax rises.
He estimated that between eight and 13 million people are not saving enough.
Charities, trade unions and business organisations have all put forward a number of possible issues and solutions.
The Equal Opportunities Commission (EOC), for example, has called for a radical approach to the problem, pointing out that women in particular do not have sufficient pensions coverage, and that the situation must be tackled.
The Commission's review panel, led by Adair Turner, a former head of the Confederation of British Industry (CBI), will outline of the scale of the problem when it publishes its first report on Tuesday. Its recommendations will then follow a year later.
Writing in the Observer newspaper, Mr Johnson called for an end to "the head in the sand culture" on Britain's pensions gap.
He estimated there are between eight and 13 million people "who are either undersaving or who might want to save more" for retirement.
Another problem, he said, is that half the population retires before reaching state pension age - 40% of private pensions go to those retiring early.
"Helping people to work longer is a crucial part of the solution", said Mr Johnson, adding that the government wants to tackle age discrimination rather than forcing people to retire later.
The shortfall in pension funds has been caused by a number of factors, such as stock market falls since mid-2000 and longer life expectancy.
There are about 17 million baby boomers born after the Second World War who will reach retirement during the next 10 years.
"There are problems building up in about 15 or 20 years' time," said Mr Johnson.
While the government says the pensions gap is caused by a mix of undersaving and early retirement, the Conservative Party has blamed Chancellor Gordon Brown's removal of pensions tax breaks in his first budget.
Shadow Pensions Secretary David Willetts said the leaks confirmed just how bad the pensions crisis had become.
"If nothing is done to put this right, retirement will fall a long way short of our expectations," said Mr Willetts.
"We must reverse the spread of means-testing, strengthen company pensions and provide better incentives for saving."
Mr Willetts went on to outline the Conservative's eight point pensions action plan, which includes linking the basic state pensions to earnings rather than prices.
The Trades Union Congress (TUC) has called for all employers to be made to contribute to their staff's pensions, while the Confederation of British Industry (CBI) takes an opposing view, saying the contribution of firms has already doubled since 1997.
Other bodies, such as financial organisation Mellon, believe the pensions issue should be taken out of political hands.
Mellon has called for the establishment of a new independent pensions authority comprising experts from the pensions industry.
Much as the Bank of England sets interest rates, Mellon says it should be given freedom to draft legislation, placing a greater weight upon the views of full-time pensions experts, rather than politicians.