Bank of Scotland was the most complained-about mortgage and home finance firm in H2 2017, according to the Financial Ombudsman Service.
The latest FOS figures show the Lloyds Banking Group arm had 559 new claims made against it.
Santander UK was second with 520, while Barclays UK logged 320.
Nationwide had 276 such grievances taken up by the complaints watchdog and RBS’s NatWest division had 270.
Loan administration firm Elderbridge had the most upheld FOS complaints against it, with 46 per cent found in consumers’ favour.
Royal Bank of Scotland and Mortgage Express both had 32 per cent of claims upheld against them.
NRAM, formerly Northern Rock, had 30 per cent of grievances confirmed against it by the FOS, as did NatWest.
The average for all businesses is 24 per cent of complaints upheld.
The ‘mortgage and home finance’ category includes complaints against house mortgages, home income plans, home purchase plans and sale and rent back.
Pension mortgages falls under the ‘life and pensions’ category. Mortgage endowment grievances fall under the ‘investments’ category.
However, the amount of complaints for mortgages and home finance is dwarfed by areas such as banking and credit or missold payment protection insurance.
For example, the FOS registered 17,119 new PPI complaints against Bank of Scotland alone in H2 2017. This is more than all mortgage complaints against all financial firms during the period.