The headquarters of HSBC bank in London's Canary Wharf financial district in slight morning mist early March 11, 2016.REUTERS/Russell Boyce

LONDON (Reuters) - Three of Britain’s largest banks are planning to close about 400 branches this year, according to people familiar with the situation, a new program of closures that could leave thousands of customers without easy access to a bank.

The number of branches operated by the major banking groups in the UK has halved in the last 20 years and following political pressure a new rule was set last year that requires banks to assess the impact on local communities of a branch closure. HSBC HSBA.L may close the highest number with about 200 branches set to go this year, the people said. That is about a fifth of the bank's UK branches and a third more than it closed last year.Royal Bank of Scotland RBS.L and Barclays BARC.L are also planning to close about 100 branches each, the people said."The bank closures will accelerate the death of the British high street," said Derek French, director of the Campaign for Community Banking. "This will particularly have a knock on impact on local businesses and the elderly."

HSBC, RBS and Barclays said in separate statements they were reducing their branch networks as customers visit less frequently in favor of banking online or via mobile.

Each bank said they had put in place measures to mitigate customer concerns, with HSBC forming a partnership with the Post Office and Barclays linking up with supermarket chain ASDA WMT.N to continue offering services.While banks argue the need to maintain extensive branch networks has fallen sharply in recent years as customers increasingly bank online, critics say local branches provide a vital service and that elderly and low income customers are hit hardest by closures as many do not have internet access.

About 70 percent of Britons still say it is important to have a bank branch close to where they live, according to a survey of 2,010 people by research firm ComRes.

The UK had 25 bank branches per 100,000 adults at the end of 2014, according to Citigroup, below the prevailing rates in southern European countries like Spain and France of 70 and 38 respectively but above the average of 17 in the Nordic countries where online banking is more advanced.About half of the UK’s remaining 10,386 branches may disappear in the next five years as people increasingly bank online and lenders cut costs to increase profit, according to research by UBS.European and U.S. banks are expected to cut about 1.7 million jobs in the next decade due to these changes, according to the research by Citi published last week. In the last four years HSBC said the number of customers visiting branches in Britain has fallen by about 40 percent and more than 90 percent of customer contact with the bank is via the phone or internet.