There were 4.13 million complaints made to 3,161 firms during the period, a 10% increase compared with the previous six months. 98% of complaints were made to just 235 firms.

Payment protection insurance (PPI) complaints accounted for 42% of all gripes, according to the figures from the Financial Conduct Authority (FCA).

The next most complained about products were current accounts, credit cards and motor and transport insurance.

Excluding PPI, complaints increased by 9% or 193,360 from the previous six months.

The proportion of non-PPI complaints closed by firms within three business days went down from 59% to 58%.

Christopher Woolard, executive director of strategy and competition at the FCA, said:  “Firms need to be doing all that they can to reduce complaints. It is clear that firms need to look at the cause of the rise in complaints and address these issues to prevent further increases.

“It should be a priority for firms to ensure good consumer outcomes are achieved and they should be making sure that they are taking the right steps to treat customers fairly.

“We are encouraged to see that figures are showing that more consumers are making a decision on whether to complain about PPI.”

People have until 29 August 2019 to reclaim mis-sold PPI.

The FCA said last week seven million complaints have been made in the 10 months since it launched its advertising campaign promoting the deadline, which features Arnold Schwarzenegger’s animatronic head and £3.7bn has been paid out in compensation.