The Independent Project Board study follows an Office of Fair Trading probe into DC workplace pensions in 2013 which said around £30bn of savers' money was in schemes with charges which were at risk of being poor value for money.
Pensions expert Tom McPhail, of Hargreaves Lansdown, said today's report showed billions of pounds of investors' life savings were "still languishing in poor value products".
The audit of charges and benefits in legacy schemes found many schemes above the auto-enrolment cap, which is set at 0.75%.
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The report stated: "Between £23.2bn and £25.8bn of AUM is potentially exposed to charges of above 1%. Around half of this is potentially exposed to charges above 1.5%; between £5.6bn and £8.0bn is potentially exposed to charges above 2%; and around £0.9bn is potentially exposed to charges above 3%.
"The majority of the AUM exposed to charges over 3% (£0.7bn out of £0.9bn) is held by savers with pots of less than £10k.
"Of this, over 90% is held by savers that are paid-up and have stopped contributing. For such savers the impact of monthly fees can result in a very high impact of charges.
"Schemes where savers are potentially exposed to the very highest charges are more likely to have complex charge structures.
"Nearly all AUM potentially exposed to charges of over 3% are in schemes with monthly fees or deductions from contributions."
It estimated there are 407,000 savers that have joined schemes in the last three years who could be exposed to a charge of over 1% in the future.
Of these, 178,000 could be exposed to charges over 2% and 22,000 to charges over 3%.
Officials found £3.4bn of AUM with potential exit charges of 10% if savers leave their scheme today. Of this, £0.8bn is held by savers over age 55, who will be eligible to withdraw their pension savings from April 2015.
The IPB, which was set up by the Association of British Insurers, will tell providers of each scheme where savers are potentially exposed to high charges to take action to improve outcomes for savers. It will also demand data and any further analysis and proposed actions are sent to the relevant governance body by the end of June 2015 at the latest.
Mr McPhail, head of pensions research at Hargreaves Lansdown, said: "Long-standing loyal investors shouldn't be penalised by getting a worse deal than new customers. This audit has revealed that billions of pounds of investors' life savings are still languishing in poor value products, and worse still, 407,000 have joined poor value schemes in the last 3 years.
"Whilst the audit committee didn't have the power to force the pension providers to put their house in order, it is clear that if they don't do it of their own free will today, they may be forced to tomorrow."
The IPB recommended the Department for Work and Pensions and the Financial Conduct Authority should jointly review industry-wide progress in remedying poor value schemes and publish a report by the end of 2016.
Carol Sergeant, chair of the Independent Project Board, said: "This audit has highlighted the importance of understanding the impact of scheme design on individual savers and has shown that there is no "one size fits all" charge structure that will ensure all savers get value for money all of the time.
"The comprehensive data set and the wide range of scenarios we have used in the analysis will help governance bodies to determine whether their scheme members are receiving value for money and will enable them to recommend changes to providers where they are not." 

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