Big Ben falls out of time

Big Ben has become "temperamental" and can be off by off by up to six seconds because it is so old, Parliament's clocksmiths have admitted.

For the past fortnight the 156-year-old clock's chimes and bongs which signify the passing of the hour have been fast, interrupting broadcasts of BBC Radio 4's PM programme.

The Houses of Parliament's three dedicated clocksmiths were dispatched to deal with the problem by removing weights from the pendulum.

They admit, however, that they "don't know why it has happened" and that the clocks age means that it "fits every now and then".

Steve Jaggs, the keeper of the clock, told the PM programme: "We carry out regular checks because this is a mechanical cost. It does take a lot of love and care. We have got three highly skilled members of staff dedicated to looking after all the clocks. They were dispatched immediately."

Ian Westworth, one of the three clocksmiths, said: "The error started building up and went slightly unnoticed over a weekend.

"You can't just wind the hands forward. You have to make a very gradual change by adding coins to speed the clock up or taking weight off to slow it back down again.

"We don't know why it happened. You're talking about a 156-year-old clock, it does have a little fit every now and then. It's a little temperamental.

"Imagine running your car for 24 hours a day, 365 days a year for the last 156 years."

When the team corrected the clock, however, it started going too slowly. Mr Westworth said: "When we started correcting it it corrected itself at the same time. It went from being fast to being slow. We have been up their most days just getting it right."

He added: "Traditionally we have to go up three times a week to wind the clock. We phone up the speaking clock and at five minutes to the hour, start a stopwatch, go up to the belfry, stand by the bell and the hammer. As it strikes the bell we'll stop the stopwatch. We can tell if it's going slightly fast or slow."

Surveyors hired by the Commons Commission - a group of MPs chaired by John Bercow, the Commons Speaker - previously found major subsidence in Westminster Palace, partly as a result of the digging of the Jubilee Line in the 1990s.

The report said that the Big Ben clock tower is tilting 18in from the vertical and cracks have appeared in the walls of the Palace. The building also has electrical problems, fire risks and multiple safety hazards.

Installed in 1859, each clock face is made up of 312 pieces of opal glass set in a cast iron frame.

Big Ben was cleaned last year for the first time since 2010. A team of abseilers had not just the height – 315ft – to contend with, but the fact that the glass panels are extremely thin and fragile because the dials were once lit by dim gaslight.

The operation took four days, with one face of the clock scrubbed each day. Essential maintenance of the mechanism is also carried out as each face of the clock is stopped.