Britain's big banks could face a shake-up after the country's competition watchdog launched a probe into the industry.The banks' personal current accounts and small business banking were "not working well for customers", the Competition & Markets Authority (CMA) said in a statement.The CMA said it had provisionally decided to consult on plans for "a joined up in-depth market investigation" into the markets for personal current accounts with revenues of more than £8bn and banking for small firms, including the £2bn-plus business current account market and business loans.The regulator can order structural remedies, such as breaking up over-dominant banks and telling them to improve information given to customers.The CMA has proposed moves to boost competition such as making the authorisation regime for new banks simpler and faster, making switching easier and improving transparency.But it said its research had found problems such as significant barriers to entry and expansion for newer and smaller banks and concentrated markets, particularly in Scotland and Northern Ireland.It said there was very little movement in the market share of the largest banks other than as a result of mergers and acquisitions.The CMA added that many customers could not see much difference between the largest banks in terms of the services they offer and levels of shopping around and switching between banks remain low.CMA Chief Executive Alex Chisholm said: "Our studies have found that despite some positive developments, significant competition concerns remain which mean that customers may not be getting consistently good service and value from their banks."Our provisional view is that a full market investigation by an independent, expert CMA group is necessary to look at this market in detail and identify appropriate measures if competition concerns are found. However we very much welcome views, which we will carefully consider, before taking a final decision."Shares in Royal Bank of Scotland and Lloyds Banking Group, which have big involvement in personal and small business banking, fell 6p to 317.7p and 0.37p to 72.8p respectively by 10:06 in London.PW