The service saw 40,000 queries a week resulting in 512,167 new complaints during the past 12 months.

In its annual review for 2013/14, the service said it answered 2.3m enquiries from consumers and settled a record 518,778 disputes – more than double the number last year.

Payment protection insurance (PPI) made up 78 per cent of all cases, with the number of PPI complaints rising 6 per cent to 399,939.

Chief ombudsman Tony Boorman said: “It’s been an unprecedented 12 months for the ombudsman by anyone’s standards. Complaints continued at record levels – and we resolved over half a million cases during the year.

“But our work – and complaints handling in general – is about much more than closing cases and reporting big numbers.”

He added: “Each case we see tells a story about the lives and livelihoods of the individuals involved. In our experience, people are simply looking for honest, straightforward answers that show someone has listened and helped make sense of things.

“So whether it’s dealing with a complex pension complaint or problems with a mobile banking app, the financial services sector continues to face the challenge of putting the customer at the centre of their business.”

FOS said in 58 per cent of the cases it resolved it found in the consumer’s favour.

Almost a quarter of the enquiries it received were about general financial problems and concerns – and weren’t product-specific. And about one in five initial enquiries turned into a formal dispute – a record 512,167 new complaints.

Four of the UK’s largest banking groups accounted for 63 per cent of all complaints received. Other than PPI, it resolved seven out of ten (71 per cent) complaints within six months.