Complaints against high street banks have risen by almost a half over the last year, according to Britain's banking industry watchdog.

The Banking Codes Standards Board (BCSB), which operates a voluntary industry code of conduct, received 3,500 public complaints and enquiries in 2005 – double the amount received in 2004.

A recent report from the BCSB revealed 1,200 complaints were received in just six months between January and October 2005 and most of these complaints were concerned with interest rates and penalty charges.

Customers are also increasingly worried about security, incidences of bank error, missing transactions and one in ten were upset with the way banks dealt with their complaints.

The report has been released only weeks after the biggest banks announced combined annual profits totalling more than £30 billion.

Voicing concerns that the number of complaints could represent a much wider problem, the industry watchdog said: "Given the BCSB is often contacted only as the last resort, we were concerned that our figures could be the tip of an iceberg."

The watchdog said it is now up to the Financial Services Authority (FSA) to decide whether to take action against banks which do not make efforts to improve their handling of customer complaints.