Almost 11 million Brits will not have adequate incomes in retirement, Department for Work and Pensions Research shows.
The Department for Work and Pensions will not publish its proposals for state pension reform until the autumn due to the "complexity" of the system.
A conservative MP and close ally of the prime minister will today call for pensioner benefits to be means tested.
The universal state pension due to be implemented from 2015 will penalise people with additional rights accrued under the current system, a consultant warns.
Pensioners' incomes has grown faster since 1999 than those of working age people, the Institute for Fiscal Studies said.
France's new Socialist government, led by President Francois Hollande, will today present a decree that will lower the state pension age for people who started work early in life.
Labour will vote in the House of Commons against the government's planned freeze of age-related tax allowances.
State pension payments will rise to an average of £124 a week, an increase of £6 from last year, the government has said.
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