The taxpayer faces a bill of up to £7.1 billion to stop the Palace of Westminster falling down unless MPs and peers agree to move out, according to a report.
A study by independent consultants has highlighted the appalling state of Parliament - with major fire risks and the threat of roof collapses.
It proposes a series of options, from politicians staying in the famous building to a "full decant" that would see both chambers emptied and moved to temporary accommodation.
If MPs and peers remain, the necessary work will take an estimated 32 years and could cost £5.7 billion - with the possibility the figure could hit £7.1 billion.
A mid-option would see MPs and peers vacate the chambers in turn, at a cost of around £4.4 billion. Fully leaving the heritage site while it is renovated into a state-of-the art building with mod cons would take six years and cost around £3.9 billion.
A joint committee of MPs and peers will now be formed to consider the choices.
The Independent Options Appraisal (IOA) was commissioned by the parliamentary authorities in 2013 from an independent team of external experts led by Deloitte Real Estate. The study itself and associated investigations have cost around £8 million.
A statement issued by both Houses said: "The restoration and renewal of the Palace of Westminster will be a major challenge facing Parliament in the coming years and is certain to be a matter of public interest.
"The process to establish a Joint Committee, which will make recommendations to both Houses on how to proceed, is already under way. It will be for the Joint Committee to decide how best to carry out its task.”
A full restoration programme is unlikely to start before 2020.