Report for Commons Finance Committee recommends £29.2m package for dilapidated timepiece, but says the cost could rise to £40m

The taxpayer could face a bill of at least £29m to properly refurbish Big Ben’s clock and keep the famous “bongs” sounding, according to a report.

Parliament’s Great Clock is said to be so dilapidated that it could grind to a halt unless drastic repairs are carried out. A report presented to the cross-party Commons finance committee has set out a £29.2m plan for fixing the clock. It would see the mechanism shut down for four months – believed to be the longest stoppage in its 156-year history.

The document, seen by the Sunday Times and Mail on Sunday newspapers, said: “The clock currently has chronic problems with the bearings behind the hands and the pendulum. Either could become acute at any time, causing the clock to stop – or worse.”

Action is also needed to combat “severe metal erosion, cracks in the roof and other structural defects” in the Elizabeth Tower.

“There are major concerns that if this is not carried out within the next two to three years, the clock mechanism is at risk of failure with the huge risk of international reputational damage for Parliament,” the report said. “In the event of a clock-hand failure, it could take up to a year to repair due to the scaffolding needed.”

The proposed £29m full refurbishment would involve the clock being stopped for four months, and each of the four faces covered in turn as work was undertaken. A visitor centre would also be constructed at the base of the 96m (315ft) tower and a lift installed as an alternative to the 334 steps.

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The previous longest shutdown is thought to have been in 1976, when the clock stopped intermittently for 26 days over nine months while repairs were carried out.

Officials admit it would cost only £4.9m “to prevent the clock from failing”, but they suggested the cost could rise to a cumulative total of £40m if the underlying problems are not dealt with in one go.

The public purse is already facing a restoration bill of up to £7bn for the crumbling Palace of Westminster. But MPs have been told the state of the clock is so dire it has to be tackled immediately.