The mis-selling scandal has seen banks and other financial institutions pay billions in compensation to customers, and shows little signs of slowing down.
The FOS received 85,562 complaints from January to June, up 73 per cent from 49,419 in the previous six-month period.
Barclays was the worst hit, with 19,522 complaints, up 179.9 per cent.
However, once banks’ subsidiaries are included Lloyds group saw 20,232 PPI complaints, compared with Barclays group’s 19,789.
Building societies have also seen complaints – 3,892 were seen against Nationwide, up 118.9 per cent.
Customers who think they may have been mis-sold PPI can approach their banks, who have six weeks to deal with the complaint.
If they fail to meet that deadline or the customer is not satisfied with the response, they can go to the FOS.
Barclays insists it is working hard to process complaints rapidly.
“We have worked hard to improve our complaints handling and are seeing fewer customers feeling the need to go to the FOS,” said Barclays’ Paul Maddox. “Excluding PPI, complaints to the FOS about Barclays are down eight per cent to 4,668, the lowest level for three years.”
Lloyds also noted that non-PPI complaints had fallen 14 per cent to 7,513, while HSBC insisted that the “vast majority” of its 15m UK customers are “very happy” with its service. Meanwhile RBS believes it is over half way through dealing with all the expected complaints.