The cost of repairing the Elizabeth Tower, which houses the famous Big Ben bell, has risen by £18.6m.
Parliamentary authorities were told that an extra £18.6m was needed following the discovery of extensive Second World War bomb damage, pollution and asbestos.
The new costs would see the renovation bill rise by almost a third from £61.1m to £79.7m.
However, a spokesman for the House of Commons Commission said members were “extremely disappointed” by the request for “yet more funding”.
“It is very frustrating to learn that the Elizabeth Tower project requires yet more funding, having agreed an extra £32 million in 2017,” he said.
“We have requested more detailed information about the lessons learned from this experience – as well as assurances that more robust estimates are prepared for works of this nature in the future.”
Ian Ailles, director-general of the House of Commons, said the Elizabeth Tower restoration – which began in 2017 and is scheduled to continue until next year – “had been more complex than we could have anticipated”.
He explained that it had not been possible to understand the “full extent of the damage” until scaffolding had gone up and a survey was carried out.
The examination revealed:
- decay and damage to hundreds of intricate carvings
- asbestos in the belfry
- extensive use of toxic lead paint
- broken glass in the clock dials
- the need for a specialist clock expert
The four clock dials on the outside of the tower contain a total of 1,296 individual pieces of glass, each of which need to be replaced as part of the restoration work.
The clock – which weighs 12 tonnes – has been dismantled and taken away for a complete overhaul.
And 700 stone repairs have been needed – 300 more than the initial estimate – and every new piece of stone needs to be painstakingly recarved.
The Elizabeth Tower is often mistakenly called Big Ben by tourists and Londoners alike – but that latter name only refers to the bell that occupies part of it.
The tower only gained its current name, having previously been called the Clock Tower, when it was renamed in honour of the Queen to mark her diamond jubilee in 2012.