The number of people saving into a company pension scheme has fallen from 6.3 million to 3.2 million since 1991, the Office for National Statistics (ONS) says.
The current figures are boosted by the larger and more generous pension schemes of the Post Office and the BBC, which were reclassified as private sector in 2000.
Personal pension contributions also fell, in particular between 2007 and 2010.
Total contributions into personal pensions, including those from employers, fell from £20.8bn in 2007-08 to £18.7bn in 2009-10.
The sharpest fall was in contributions by individuals to their personal pensions. In 2007-08 individual savers paid in £10.2bn, but in 2009-10, they paid in just £8bn.
Darren Philp, of the National Association of Pension Funds (NAPF), said: "These trends reflect the current state of the economy and the impact this is having on UK households.
"The auto-enrolment reforms being introduced from next year are likely to result in 5 to 9 million people starting to save into a pension or save more."
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