Government-owned lender Northern Rock Asset Management / NRAM, or the so-called bad bank housing ex-Northern Rock assets, emerged in fourth place with Barclays in fifth.
The sixth-monthly Financial Conduct Authority complaints data showed finance institutions including banks and mutuals received 2.11 million complaints in the second half of 2015.
Overall, the number of complaints fell 1.4% against the previous six months, mainly due to the 10% fall in current account complaints and 15% drop on savings.
Payment Protection Insurance (PPI) is still by far the most-complained-about product with 1.17 million consumers angry enough to report issues to the provider.
Christopher Woolard, director of strategy and competition at the FCA, said: “Firms seem to have taken on board our previous feedback on levels of complaints and we are slowly seeing firms address these issues.
“However, firms still need to do all they can to reduce complaints and ensure that they are working in the best interests of consumers.”
Consumers received compensation of £1.97bn between July and December, a slight fall from £1.98bn in H1.
Banking and credit card complaints rose by 27% and the top five most-complained about products include, PPI up 6% at 932,298, current accounts down on H1 at 454,276 and general insurance also down to 296,505.
Firms will be obliged to list complaint numbers contextualised by number of customers and accounts on their own websites from February 2017.
Overall, the five firms which received the most personal finance-related complaints are, in order, Barclays Bank, Lloyds, Bank of Scotland, National Westminster Bank and HSBC.
Woolard added: “Firms still need to do all they can to reduce complaints and ensure that they are working in the best interests of consumers.”
