Barclays was the most complained about firm for investment products during the second half of 2011.
The group reported 3,284 complaints in the second half of the year, far ahead of second-placed Santander UK, which reported 1,956 complaints during the same period.
Most complained about firms for investment products
Vanquis Bank and Guardian Assurance had the highest percentage of complaints upheld by the firm at 80%, followed by Scottish Widows Unit Trust Managers with 79%.
Yorkshire Building Society had the lowest level of complaints upheld, reporting just 6% of closed complaints were upheld.