Restoring the crumbling Houses of Parliament could cost more than £39bn and take between 38 and 61 years to complete, parliamentarians have been told.
It's one of two proposals being considered by MPs and peers, and would see work on the building, which mostly dates from the Victorian era, completed in stages.
Under the second option presented by the restoration and renewal client board, both houses would leave the Palace of Westminster for between 19 and 24 years while works take place at a cost of up to £15.6bn.
The client board, which is made up of members of the commissions of both Houses of Parliament, warned in a statement on Thursday that a decision on starting restoration work "is needed now".
It said the site's fabric and services "have deteriorated and require substantial repair or replacement", adding: "We are beyond the point where putting off these major works is sustainable."
MPs and peers have also been asked to agree to initial restoration works at the Houses of Parliament lasting seven years, at a cost of up to £3bn.
That work could start in 2026 if approved with a motion from both Houses.
The board will then ask them to choose between the final two options by mid-2030.
Repairing the inside of the Victoria Tower, building a jetty on the Thames for deliveries by river, and starting underground construction on tunnel shafts are all part of the first phase.
If it's decided to move out fully, Commons business will start to be transferred to the so-called Northern Estate - outside the palace but close by - and the Lords to the nearby QEII conference centre from 2032.
Current repair costs 'unsustainable'
Repairs and maintenance of the Palace of Westminster currently runs at a cost of £1.5m a week, which is "unsustainable", according to the proposals.
Heating in a large part of the House of Lords is set to fail and there are significant problems with the sewage system.
Since 2016, there have been 36 fire incidents, 12 asbestos incidents and 19 stone-masonry incidents.
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The debate over how to revamp the Houses of Parliament has been ongoing for years due to the expected cost of the project and concerns about the condition of the historic buildings on the World Heritage Site.
MPs and peers had agreed a plan in 2018 for both the Commons and Lords to move to temporary facilities near the existing site to allow essential repairs and upgrades to be made.
But this was subsequently revisited amid concerns about the cost.
(c) Sky News 2026: Move out of Westminster or face 60 years of repairs, MPs warned
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