Bank of Scotland is the UK's most complained about financial firm, with the number of disgruntled account holders hitting a record high.

The equivalent of more than 300 customers of both Bank of Scotland and Halifax complained every day during the first six months of the year. Figures from the Financial Ombudsman Service (FOS) show 61,644 complaints were lodged against the Edinburgh-based institutions between January and June.

This was up 57% on the previous six months.

The report comes as a huge payment protection insurance (PPI) mis-selling scandal continues to weigh on the industry.

At Bank of Scotland, complaints about PPI alone reached 57,680 during the first half of the year, up 68% on the previous six months.

Of the PPI cases looked at, almost nine out of 10 (87%) were upheld. The bank said the figures had swollen after it decided to pay a large number of customers with cases pending.

A spokesman said: "This has had a significant impact on the FOS data, so we are confident the change rate on PPI complaints will reduce significantly as we continue to work with FOS in the second half of the year."

Lloyds TSB Bank had the second-highest level of overall complaints at 59,753. Royal Bank of Scotland was the seventh most complained about financial business. It dealt with 11,268 cases over the same six-month period.

Complaints about PPI made up more than eight in 10 of those received by the ombudsman.

The ombudsman said some lenders continue to drag their heels on repaying mis-sold PPI. FOS chief executive Natalie Ceeney said: "We are still seeing cases where businesses are not following our long-standing approach to PPI, resulting in long waits and unnecessary delays for consumers."