The Bank of Scotland was the most complained-about home finance firm in the second half of 2015, according to the FCA.
FCA complaints data shows the bank had 11,606 grievances logged against it in the period.
The home finance category includes mortgages and equity release.
Santander UK had 7,331 complaints, HSBC Bank 6,296, NRAM 6,107 an Barclays Bank 5,740.
The FCA says it had 67,546 complaints in its ‘savings’ category, down 15 per cent on the previous six months.
The category includes cash ISAs and other banking complaints.
There were 36,963 investment complaints, down 20 per cent from 46,019 in the first half of 2015.
Complaints related to Peps and Isas (excluding cash Isas) were down 15 per cent compared to the first half of 2015, from 13,976 to 11,848, while complaints related to investment bonds continued to decline and are almost half what they were in the first half of 2011 (6,202 from 12,306).
However, the FCA notes the decline in complaints about investment bonds was consistent with a decrease in sales in the category.
HSBC saw the most investment complaints, at 3,007, followed by Barclays at 2,880, and Equiniti Financial Services at 1,567.
Across all categories included in the FCA data, complaints were down 1.4 per cent to 2,106,155 from 2,135,508 in the first half of 2015, and this decline was more marked when PPI data was excluded. It received 1,244,937 complaints, up 6 per cent from 1,201,876 in 2015 H1.
The decrease was mostly driven by a 10 per cent drop in complaints about current accounts and a 15 per cent drop in complaints about savings accounts.
Investments only accounted for 2 per cent of all complaints, compared to general insurance and pure protection, which accounted for 59 per cent, while banking and credit cards accounted for 32 per cent.
Last July, the FCA announced it was changing its complaint handling rules to make them “less bureaucratic” for firms and easier for consumers, and to provide the regulator with improved intelligence on complaints.
The change means that complaint data released from March 2017 will not be comparable to data released before this period.