Banks could be forced to admit to the number of complaints received from customers under proposals from the City watchdog.

The Financial Services Authority (FSA) wants to name and shame firms that have frustrated customers by publishing lists on the most complained about products every six months in a move to increase transparency.

It said consumers should also be able to find out how many complaints a firm has opened and closed, the number that were resolved within eight weeks and the percentage of complaints that were upheld.

Banks and building societies will have to provide the data every six months, which will be collated and published by the FSA.

The FSA will not require firms to publish the details of complaints that have been resolved the following day.

The proposals were mentioned in a white paper on banking reform, released yesterday, which also included demands for banks to handle consumer complaints more effectively before they reach the Financial Ombudsman Service (FOS).

The FOS has received soaring numbers of complaints over recent years and expects its case load to rise to 150,000 by 2009-10. In 2001 the ombudsman received 31,347 complains. Last year more than half of complaints to the FOS related to just six financial groups.

The white paper also included plans to enable large groups of consumers affected by the same problem to take more “collective action" with the help of a new Consumer Advocate, who will be appointed next year.

Dan Waters, the FSA’s director of retail policy and conduct risk, said: “Transparency is an important regulatory tool. Publishing complaints data will mean that people can learn more about how firms handle complaints and the frequency with which they arise.

"We also consider that publishing this information will incentivise firms to deal more effectively with complaints and help to raise industry standards in this important area. It is essential that the information is meaningful and genuinely brings benefits by enhancing customers’ experiences of the firms they deal with.”

It will publish complaints information across banking, home finance, general insurance and pure protection, life and pensions and investments.