The number of complaints about structured products leapt by 40 per cent between June and December last year.
FSA complaint data, which was published last week, shows there were 1,692 complaints about structured products over the second half of last year compared with 1,219 in the previous six months.
Overall, complaints about investments fell by 6 per cent from 43,605 in the first half of 2011 to 40,972 in the second half.
Complaints about decumulation, life and pensions dropped by 4 per cent from 81,563 to 78,076.
Complaints related to investment management and investment services, including platforms, increased by 8 per cent from 4,787 to 5,151.
Personal pension complaints were relatively flat at 23,098 while income drawdown complaints dropped by 5 per cent from 1,042 to 989.
Equity-release complaints rose by 20 per cent from 439 to 530.
Barclays Bank had the most investment complaints, with a total of 3,284. It upheld 37 per cent of investment complaints it closed in the second half of 2011.
Aviva received the most decumulation, life and pensions complaints with 8,807, and upheld 54 per cent.
Across all the financial services firms included in the data, 44 per cent of both investment and decumulation, life and pension complaints were upheld.
Clearwater Financial Planning managing director Duncan Carter says: “With interest rates being as low as they are, people are seeing the headline income rate of structured products and buying into them without realising what they have bought.”