Complaints to the Financial Ombudsman more than doubled in the second half of 2012 to a record 283,251, a 110 per cent increase over the first six months.
Three-quarters of the complaints were about mis-sold payment protection insurance (PPI), with Lloyds TSB the most complained-about brand. It had 45,727 complaints, after the number of PPI claims rose 344 per cent.
However the number of upheld complaints fell dramatically, from 74 per cent to 55 per cent.
In second place was Barclays with 44,725 complaints. The number upheld climbed from 53 per cent to 57 per cent.
Lloyds-owned Bank of Scotland saw an increase in PPI complaints of 731 per cent, pushing it to third place in the list with 39,375.
The number of upheld PPI complaints varied enormously. Black Horse had 97 per cent upheld, Capital One just 6 per cent.