A provisional decision on what remedies to take to boost competition was originally due next month after a review was launched in November 2014, but this will not now be published as planned, the Competition and Markets Authority said.

The probe marks Britain's latest effort to reduce the dominance of its main banks, which include HSBC (>> HSBC Holdings plc), Royal Bank of Scotland (>> Royal Bank of Scotland Group plc), Barclays (>> Barclays PLC) and Lloyds (>> Lloyds Banking Group PLC).

Alasdair Smith, who chairs the investigation, said a number of new suggestions had been made, including proposals to help current account customers with overdrafts.

"We therefore expect that an extension will be necessary to give us a bit more time for analysis and consultation."

When it launched the review the watchdog said banks had not done enough to meet the needs of retail customers or small and medium-sized businesses.

The watchdog has the power to order banks to sell assets or to provide greater clarity on pricing.

It has been consulting on possible remedies to promote competition since they were published in October last year. These included measures to make it easier for customers to compare bank products and review the services they receive.

The CMA will now decide on how much more time it needs by early March, when it will produce a timetable for publication of its final report and also its provisional decision on remedies.

(Reporting by Jane Merriman; Editing by Alexander Smith)