The repair bill for Big Ben's home Elizabeth Tower is set to rise by millions of pounds, it has been revealed.
There could be a cost increase of £18.6 million, parliamentary authorities were told in February 2020.
If the latest estimates are correct, it would see the new budget increased by almost a third from £61.1 million to £79.7 million.
To put it in context, the extra £18.6 million needed to complete the works is almost as much as the £20 million the government has pledged to fight coronavirus.
The discovery of asbestos and extensive World War II bomb damage to the 177-year-old Elizabeth Tower are among the reasons for the bigger bill.
However, a House of Commons Commission spokesman said its members were "extremely disappointed" by the request for "yet more funding".
The complexity of the repairs was also partly the reason why a bid to get Big Ben to bong on Brexit day was unsuccessful, with the cost of getting the bell to work by the deadline set at £500,000.
The StandUp4Brexit group managed to crowdfund £272,000 in a bid to make it ring - which has instead gone to veterans' charity Help for Heroes.
Given the latest cost hike, the Evening Standard explores the Big Ben restoration below...
When did work on the Elizabeth Tower start?
Work on the tower began on Monday, August 21 at noon.
Members of the public gathered in Parliament Square to mark the moment Big Ben's hourly bongs were silenced for a proposed four years.
What was the initial budget?
Prior to starting, the repair work was initially priced at £29 million.
However, by September 2017 unforeseen conservation costs and unexpected conditions around the tower had more than doubled the cost to £61 million.
The new figure included £45 million of restoration costs with an additional £16m for risk, VAT and fire safety.
How much has been spent on the repairs so far?
Renovation is still underway however, an additional £18.6 million has been requested from the public purse to complete the works.
It is not public knowledge how much of the former £61.1 million price tag gas been used already.
But, it seems works would not be able to be completed unless the latest proposed cash injection is approved.
The new budget will be set if it is approved by the accounting officers of the two houses.
When are the Big Ben repairs due to end?
Big Ben is silenced for four years
The repair works started in 2017 and were due to end in 2021.
The completion date does not appear to have been extended.
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Ian Ailles, director-general of the House of Commons, said the works are proving “more complex than we could have anticipated”.
The full extent of the damage to the Tower was impossible until the scaffolding was up, he said.
Mr Ailles said: "Impact of often inappropriate conservation methods used by our predecessors, the corrosive levels of pollution in the atmosphere and the discovery of asbestos in unexpected places, we have only now been able to fully understand the full investment required for this project.”