Parliament's clock maker reveals why Big Ben went wrong

The bongs of Big Ben have been ringing at the wrong time over the past fortnight, parliament's clocksmiths have admitted.

The 156-year-old Great Clock has been out by up to six seconds causing issues for BBC Radio 4's PM programme which broadcasts the chimes live.

On 21 August the chimes ran too late, causing a short period of silence during the programme.

The Palace of Westminster's clock maker Paul Roberson said the clock could have gone wrong for a number of reasons such as changes in temperature and air pressure.

Clocksmiths have been able to gradually correct the time and say it is now accurate to less than one second.