It's Britain's most famous clock and its bongs are renowned for signalling the countdown to New Year and television's News at Ten.
But staff at Big Ben, which is more than 150 years old, have developed a novel strategy to ensure it shows the right time. They ring the speaking clock.
Employees at the Palace of Westminster called the premium-rate service more than 2,000 times last year to check the accuracy of Big Ben, The Mail on Sunday can reveal after a Freedom of Information request.
Timepiece: Employees at the Palace of Westminster called the speaking clock more than 2,000 times last year to check the accuracy of Big Ben
Engineers from Elizabeth Tower – as it was officially renamed last year in honour of the Queen's Diamond Jubilee – have rung up a bill of at least £680 ringing the speaking clock, which costs a minimum of 31p for each call from a landline and is available free on the internet.
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Sara Mendes da Costa, 46, the voice of the speaking clock, said: 'If you're looking for the absolute accurate time, the speaking clock is the one to go by.'