Theresa May, home secretary, is opposing government efforts to make it easier for Chinese tourists to obtain UK visas by warning it would present a national security risk, according to a letter sent by her staff to the prime minister’s office.

The letter, leaked to the Daily Telegraph, emerged only a day after culture secretary Jeremy Hunt unveiled an ￡8m marketing strategy to treble the number of Chinese visitors to the UK by 2015 after Britain’s success hosting the Olympics.

Mr Hunt admitted that the delay and complexity of obtaining a UK visa was a big barrier to Chinese visitors, who are able to obtain a visa to visit Europe’s Schengen countries, including France and Germany, much more easily. He told reporters that one option was to design a “parallel process” whereby Chinese tour groups could apply for a British and Schengen visa at the same time.