Non-workplace pensions are being put under the spotlight by the City regulator, which wants to know whether competition is working in the sector.
These types of pensions, also known as individual private pensions, collectively represent around £400 billion assets under management, the Financial Conduct Authority (FCA) estimates.
Research suggests that at least one in four adults have accumulated benefits in non-workplace pensions.
The FCA is seeking feedback to better understand the market for non-workplace pensions, including whether competition is working well and if there are issues that need to be addressed to protect consumers.
Christopher Woolard, FCA executive director of strategy and competition, said, in recent years, steps have been taken to address weaknesses in the workplace pensions market.
He said: "We believe it is now right to look at the other side of the picture and assess whether competition is working in non-workplace pensions.
"A diverse group of people save into non-workplace pensions and it is a growing market. We want to hear from anyone with an interest in this subject about how they think the market is working."
Particular areas of focus for the FCA will include looking at how complex products are and whether customers can identify and freely move to more competitive products.
The FCA also said it is concerned that informal defaults may be operating in the market for non-workplace pensions that are not subject to the same protection as defaults in workplace pensions.
It will look at whether providers are competing on charges and if there are barriers to consumers identifying, and choosing, from more competitive products.
The FCA is seeking feedback by April 27.
Tom McPhail, head of policy at Hargreaves Lansdown, said: "There's evidence many investors are actively engaging with their savings, making choices about how their money is managed and invested.
"There are also understandable regulatory concerns about legacy books of business and 'forgotten pensions'. This discussion paper will be a good opportunity to explore these issues."
Tom Selby, senior analyst at AJ Bell, said: "It makes sense for the FCA to scrutinise competition in the non-workplace market.
"It is vital for the integrity of the UK pension system that savers are confident the products they invest in are value for money."