The life insurance division of St James's Place had one of the highest rates of complaints upheld of any firm in the first half of 2018.
The Financial Conduct Authority revealed St James's Place UK PLC received 924 complaints in the first half of 2018, of which 719 of these related to decumulation and pensions.
Of SJP UK's total complaints, 86.7 per cent were upheld, which made it the company with the sixth highest proportion of complaints upheld.
As a whole, when complaints against St James's Place Wealth Management are factored in, SJP received 1,602 complaints, with 678 against its wealth management division, with 282 of these relating to investments and 266 relating to decumulation and pensions.
St James's Place Wealth Management had a much lower rate of upheld complaints, at 25.5 per cent.
A spokesman for SJP said: "The higher uphold rate for St. James's Place UK plc reflects the fact that many of the complaints relate to a delay or processing error. As these are administrative matters, they are therefore more likely to be upheld when resolving for clients.
"We take our client satisfaction very seriously and regret any occasion where an error results in a correction being required, although the total number of cases is low when compared to our client base of over 600,000."
Sesame, the only other advice firm listed in the FCA's data, received 655 complaints with 259 of these relating to insurance and pure protection and 215 relating to investments.
The FCA only lists firms which receive 500 complaints in a half year or 1,000 complaints in a whole year.
Across the whole financial services sector, complaints increased for the fourth successive half year, reaching a record level of 4.13m complaints made to 3,161 firms.
Payment protection insurance (PPI) continued to be the most complained about product, accounting for 42 per cent of all complaints or 1.7m in total.
Christopher Woolard, executive director of strategy and competition at the FCA, said: "Firms need to be doing all that they can to reduce complaints.
"It is clear that firms need to look at the cause of the rise in complaints and address these issues to prevent further increases.
"It should be a priority for firms to ensure good consumer outcomes are achieved and they should be making sure that they are taking the right steps to treat customers fairly.
"We are encouraged to see that figures are showing that more consumers are making a decision on whether to complain about PPI."
Amid replatforming woes at Aegon and Aviva the number of complaints relating to platforms continued to increase, reaching 12,510 in the first half of 2018, up from 11,084 in the previous half.
The Big Four banks dominated the number of complaints received during the first half of the year and were all in the top four positions, with Barclays receiving the most at 426,361.
Aviva received most complaints relating to decumulation and pensions at 8,944 while Barclays received the most complaints about investments, with 5,869.