The total of cost of repairs needed to save the crumbling Houses of Parliament could top £7.1bn.
And every taxpayer in Britain will have to pay up to £240 to fund the restoration of the Palace of Westminster, which contains both the House of Commons and the House of Lords, unless MPs agree to move out for at least six years while the work takes place.
A new Independent Options Appraisal report on the condition of the Grade 1-listed building reveals that the site is suffering major dilapidation including crumbling stonework and leaking roofs.
There are problems with asbestos and inadequate fire safety measures mean if a blaze broke out it could rip through the entire building.
There is now an increasing risk of “catastrophic failure” – such as flooding knocking out power supplies – as Parliament’s mechanical and electrical infrastructure is “no longer fit for purpose”, the independent study by Deloitte’s real estate division found.
The Unesco world heritage site has not undergone any major work since 1834 when the Old Palace was destroyed by fire.
The report, which was commissioned by parliament and conducted with architecture firms AECOM and HOK, puts forward three options for carrying out the work needed.
The cheapest option would cost £3.5bn – or £118 for every income tax-payer – but would force MPs and peers to move into temporary accommodation for six years.
However, the report suggests that this option could allow the MPs and peers to make other upgrades to the Palace of Westminster at an additional cost of about £400m.
This could include a new 10-storey lift to take MPs and members of the public up the Elizabeth Tower, which houses Big Ben, landscaping courtyards and improving banqueting facilities.
If MPs insist on remaining on site while restoration work is carried out costs are estimated at £5.7bn but could rise to £7.1bn over the 32 years it is forecast the repairs would take to complete.
A compromise option, in which MPs and then Lords moved in turn to temporary accommodation outside the Palace, would cost about £3.9bn and take 11 years to complete.
A joint committee of MPs and peers will be formed to consider the choices. Work under any of the choices put forward is not expected to begin until 2020.
Dr Richard Ware, programme director for Palace of Westminster Restoration and Renewal, said: “The Palace has reached a turning point in its history, with many features needing major renovation.
“It is clear from this report that Parliament is faced with some difficult choices. It will now consider the recommendations of the IOA and will do everything possible to secure value for money and ensure transparency throughout the process.”