Just 12% of private sector defined benefit (DB) schemes remain open to new members, according to the Pension Protection Fund (PPF).
Meanwhile, just 47% remain open to future accrual, the lifeboat fund's Purple Book 2017 revealed - three percentage points down from the 2016 and the steepest fall since 2013 when there was also a three percentage point fall in the number open to accrual.
These 47% of schemes represent around 55% of all 10.5 million private sector DB members, with another 21% in schemes which remain open to new members.
Larger schemes were most likely to be open to new members, with 19% of schemes with 10,000 or more members or between 5,000 and 9,999 members still accepting new recruits.
Meanwhile, 61% of schemes with over 10,000 members and 51% of schemes with between 5,000 and 9,999 members remained open to future accrual.
The Purple Book covers around 10.5 million members across 5,588 schemes in the PPF-eligible universe, representing 98.5% of the 5,671 total schemes.
PPF chief financial officer Andy McKinnon said the figures were unsurprising given the past few years of data.
"The picture that we see is a continuing picture of schemes closing to new accrual," he said. "There's a relatively steady trend of schemes that have stayed open, but what we are considering to see is schemes that remain open to new accrual are also closing to new members.
"As well as schemes closing to accrual, we have seen a significant trend in the decline in the number of active members."
Only 12% of DB members remain active, according to the analysis, representing around 1.3 million of all PPF-eligible savers. This is one percentage point lower than last year, which also followed a three percentage point fall from 2015.
Royal London director of policy and former pensions minister Sir Steve Webb said the figures show a stark difference from the membership in public sector DB schemes.
The most recent Office for National Statistics (ONS) showed there were 5.7 million active DB members in the public sector in 2016.
"These latest figures show a deepening divide between public and private sector workers when it comes to membership of salary-related pension schemes," Webb said. "Private sector employers are voting with their feet, closing schemes both to new workers and to existing scheme members.
"Membership of salary-related schemes in the private sector has slumped by nearly two-thirds over little more than a decade. By contrast, the number of public sector workers building up salary-related rights has actually risen in the last decade."
The figures come as a Hymans Robertson analysis predicted all FTSE 350 DB schemes will have closed to future accrual by 2027.
Nearly every trustee is confident of the next stage in their scheme’s strategy, despite almost an equal number being forced to consider replacing plans within the prior 12 months, according to research by Barnett Waddingham.
Companies could be overstating their pension liabilities by up to £60bn due to their life expectancy assumptions, according to XPS Pensions Group.
Defined benefit (DB) schemes that provide GMPs must revisit and, where necessary, top-up historic cash equivalent transfer values (CETVs) that have been calculated on an unequal basis, a landmark court judgment said last week.
Regulators must act now to impose some "proper regulation" to stop another defined benefit (DB) transfer advice disaster, saysTim Sargisson.
Opportunities for defined benefit (DB) schemes to pursue investment approaches that help repair the UK’s economy cannot stand in the way of improving member outcomes, Aegon says.