Bank of Scotland, which incorporates Halifax and BM Solutions, has topped the mortgage complaints list for the third year running.
Figures released by the Financial Ombudsman Service last week show Bank of Scotland received 590 complaints relating to mortgages and home finance in the first six months of the year, with 47% upheld in favour of consumers.
It has topped the list since 2009 when FOS first started to name and shame companies.
FOS has seen a 4% rise in the overall number of mortgage complaints in the first six months of the year. It received 3,779 complaints, up from 3,646 in the last six months of 2010.
The percentage of cases upheld in favour of consumers has also increased, from 36% to 38%.
Santander UK received the second highest number of complaints at 460, with 31% upheld in favour of consumers. This was followed by Barclays which received 362 with 45% upheld.
Other lenders in the complaints table include Northern Rock Asset Management with 212 complaints and 34% upheld, Openwork 23 with 43% upheld, Sesame had 17 relating to mortgages with 56% upheld.
FOS says it cannot comment on complaints relating to individual firms, but says administrative errors remain the largest area of mortgage complaint, with gripes from consumers whose applications to port their mortgage have been declined.
It also saw complaints when a lender reduced the upper age limit applying to the mortgage term or required the borrower to provide proof of retirement income.
Overall, during the six-month period FOS received 149,925 new complaints an increase of 54% on the 97,237 cases received in the second half of 2010 and 98,632 cases related to payment protection insurance.
Lloyds Banking Group was the most complained about bank overall, receiving 37,696 complaints, followed by Barclays with 19,569 and HSBC 14,071.