Finance firms attracted nearly 20,000 complaints a day in the first six months of 2012 as the massive backlash against the UK's banks continued.
The payment protection insurance mis-selling scandal accounted for the bulk of the 3.6m grievances, according to figures published by the Financial Services Authority.
PPI complaints soared 129% in the six month period. The bill to compensate customers of Britain's banks who were sold the payment cover is expected to eventually top £10bn.
After the figures were published by the City Watchdog, Consumer group Which? warned that the compensation bill could climb even higher.
Its analysis suggests that if PPI payouts continue at the same pace as the first half of 2012, Lloyds could run out of provisions by November 2012, Barclays by December 2012, RBS within the next six months, and HSBC by August next year.