The Financial Conduct Authority (FCA) said progress on compensation for so-called interest rate swaps had been slower than expected so far as it revealed only another 22 firms agreed redress deals last month out of nearly 30,000 cases being reviewed.
So far 32 offers in total have been accepted totalling £2 million.
But the FCA said it expects the number of offers to increase "rapidly" over the next few months, with banks planning to send out more than 1000 offers in October.
Martin Wheatley, chief executive of the FCA, said: "Whilst we are moving in the right direction, we expect to see the pace at which cases are resolved and redress paid quicken over the coming weeks."
The regulator has told banks it wants most customers who have opted into the review to be informed of the outcome of their case and, where applicable, receive initial offers of redress by the end of 2013.