Big Ben Great Clock’s hands, mechanism, pendulum and Elizabeth Tower need refurbishment, and failure to do so would cause “reputational damage”, a cross-party report found.
It has been 31 years since its last overhaul.
A parliamentary spokesman said: “No decisions on works, timescales or costs have been agreed.”
In its report, the Commons Finance Committee said problems had also been identified with the 156-year-old clock’s tower, including cracks in the masonry.
Upgrades were also needed to bring the building in line with health and safety regulations, it said.
The report, seen by the Mail on Sunday and Sunday Times, said: “There are major concerns that if this is not carried out…the clock mechanism is at risk of failure with the huge risk of international reputational damage for Parliament.
“In the event of a clock-hand failure, it could take up to a year to repair due to the scaffolding needed.”
‘A little fit’
Officials said it would cost £4.9m “to prevent the clock from failing”, but the report states the “full refurbishment” would cost £29m.
The addition of a visitor centre at the bottom of the tower, and installing a lift to the top could see the cost rise to £40m.
The parliamentary spokesperson said: “Committees of both Houses are currently considering the study.”
In August, Big Ben made headlines when the bongs lagged behind by six seconds, causing interruptions to BBC Radio 4, which broadcasts the sound live.
At the time, clocksmith Ian Westworth said the clock “does have a little fit every now and then” due to its age.