Anthony Thomson, founder of British bank Metro Bank, plans to launch an online bank, hoping to take advantage of a sharp decline in the number of customers using branches and challenge established rivals. Thomson, who stepped down as Metro Bank chairman in 2012, said he would lead the new venture called Atom alongside Mark Mullen, who last month resigned as chief executive of First Direct, the online bank run by HSBC. Britain’s financial regulator and lawmakers are keen to see new banks emerge to break the dominance of the country’s biggest banks – Lloyds Banking Group, Barclays, HSBC and Royal Bank of Scotland – which control about three-quarters of the personal current account market. Thomson said there is a growing trend for customers to bank online instead of in branches and the marketplace had changed dramatically since 2010, when Metro became Britain’s first new high-street bank for over a century. According to banking analysts, the number of transactions taking place inside branches was falling by about 8% a year. The biggest five British banks have cut 912 UK branches since 2007.