The campaign centers on the misselling of a product known as P.P.I. Introduced more than two decades ago, P.P.I. was supposed to give consumers, and lenders, a bit of peace of mind by covering loan repayments if a person could no longer work because of an accident, illness or disability, or if they died.

But regulators later determined that the insurance product was often improperly sold to people who did not need it, or could not qualify to use the insurance. Six years ago, the authorities took the banking industry to court.

Lenders agreed to settle, and the product is no longer being sold, but the cost of compensating people has far exceeded estimates. Banks in Britain have repaid more than 27 billion pounds, or about $35 billion, and set aside at least another £10 billion for customer redress.

The improper selling of payment protection insurance is one of several scandals that have hit the banking industry in Britain since the financial crisis that began in 2008 and weighed on the bottom lines of some of the country’s largest banks, including Barclays, Lloyds Banking Group and the Royal Bank of Scotland.

But this year, the F.C.A. adopted a deadline of Aug. 29, 2019, for the public to submit final claims for compensation and kicked off a two-year education campaign on Tuesday to spread the word.