House of Commons leader Jacob Rees-Mogg has insisted Parliament needs to “be able to justify to the taxpayer” the huge list of repairs the Palace of Westminster requires, as a survey revealed thousands of issues with the building.

More than 50 engineers, architectural surveyors, acoustics and lighting specialists, and ecologists have spent a combined 4,700 hours over Parliament’s recess periods investigating the building, and creating the most detailed record of the 150-year-old palace ever created.

In total, 2,343 rooms and spaces were examined over the summer and conference recesses, with experts recording thousands of issues including cracks in stonework, widespread water damage, and analysing the complex network of outdated electrical and mechanical systems.

MPs will be expected to decide in early 2023 how much taxpayers’ cash they are willing to spend on restoring Parliament.

Ahead of the likely expense to the public purse, Commons Leader Mr Rees-Mogg said: “We must be able to justify this project to taxpayers.

“That’s why it’s so important to understand and map out the restoration work needed to protect the building – so that the focus is on those essential works necessary to preserve the palace for future generations.”

Lords leader Baroness Evans of Bowes Park added: “This preparation survey work of the Palace of Westminster is essential to understand the extent and complexity of the programme of works required.

“In due course it will enable parliamentarians to properly scrutinise the proposed work and ensure value for money.”

Issues recorded by the surveyors include original Victorian stained-glass windows which are warping and sagging due to age, and crumbling stonework.

Work was also done to understand the origin of candle and gas light fittings, some of which were discovered to have been turned upside down when converted to electric power more than 100 years ago.

House of Commons Renewal
Surveyors inspect the House of Lords chamber during a parliamentary recess (PA)

It is thought the palace may contain the oldest still-in-use gas lighting system in the world but investigations continue to establish whether this is the case.

Surveyors also studied the enormous basement and the miles of outdated and interweaving gas, electrical, water, sewage, and heating pipes to get up-to-date records on the problems that need fixing.

In September, shadow Commons leader Thangam Debbonaire said she had taken a tour of the basement and described “high-voltage electricity lines next to the gas pipes and the wiring that goes nobody knows where”.

Mr Rees-Mogg is also understood to have visited the palace’s basement.

Even more detailed surveys are planned for the building throughout the winter and 2022, including “intrusive” surveys into its structure.

It is claimed that the Houses of Parliament Restoration and Renewal will create thousands of new jobs and apprenticeships, using both traditional and modern craft and construction skills, with a workforce from across the UK.

Sarah Johnson, chief executive of the Houses of Parliament Restoration and Renewal Sponsor Body, said: “The essential programme to restore the deteriorating Palace of Westminster will protect our world-famous Parliament for generations to come.

“These critical and complex investigations are already informing our detailed restoration plan, which will for the first time set out a true sense of the costs and timescales of the much-needed work.”