Complaints rise a third.
The Financial Ombudsman Service reported a 30 per cent hike in formal complaints to 123,089.
It is the highest number reported since the service's launch in 2001 and reverses the fall of the previous year.
Complaints about bank account charges and payment protection insurance drove the sharp annual rise.
Ombudsman chairman Sir Christopher Kelly said: "This time last year, we had hoped we were starting to see a downward trend in complaint numbers for the first time. But instead, events during the year have led to record numbers of new cases."
There was also a 27 per cent rise-to 794,648 - in the number of inquiries last year.
Most complaints were turned down bar bank charge and credit card cases - 84 and 79 per cent were upheld.
There was a near ten-fold increase in bank charge complaints in April to July last year alone - at nearly 32,000 - amid the Office of Fair Trading's High Court test case.
Complaints over health and travel insurance and some investments fell.