The Financial Ombudsman Service saw a 49 per cent increase in complaints relating to self-invested personal pensions in 2013/14.
In 2013/14 the FOS received 1,039 Sipp complaints, up from 697 complaints in 2012/13.
The FOS upheld 63 per cent of Sipp complaints in 2013/14, compared to 61 per cent the previous year, and says the majority of cases relate to advice to invest in unregulated collective investment schemes.
It says complaints about unregulated funds accounted for 75 per cent of Sipp cases last year.
The FOS says some consumers are being advised to move their retirement savings into Sipps that invest in unregulated investments such as overseas property, forestry and film schemes on the promise of tax breaks and good returns. Consumers are then later finding out they have no access to the invested funds.
The FOS says unsuitable Sipps are being sold to consumers who do not understand the risks or costs involved.
The information has been released ahead of publication of the FOS’s annual review later this week.