MPs remaining in the Palace of Westminster while essential restoration work takes place could take up to 76 years with a repair bill reaching ￡22 billion, according to a new report.

       The staggering cost to repair the Unesco World Heritage site appears in an initial assessment for action required to save the palace — which requires urgent maintenance and construction work.

       The study by the House of Parliament Restoration & Renewal Programme found that MPs remaining on the estate for the entirety of the works, with “no transfer”, could come with a price tag of ￡11-22 billion.

       With construction work being undertaken during parliamentary recesses, it is estimated the essential work to the Grade I listed building could take between 46 and 76 years.

       “In this scenario we have assumed an extended recess period (mid-July to mid-Oct), and that there would be no recall to the historic House of Commons Chamber during that period,” the report added.

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       Essential works needed on the estate include the removal of asbestos, reducing the fire risk, renewing pluming, electrics and data cables, improving energy efficiency and a backlog of repairs and conservation to the building itself.

       Just last week it emerged parliamentary staff and contractors may have been exposed to asbestos — forcing a “temporary pause in construction projects”.

       In a second scenario — a “partial decant” — business would remain within the Commons chamber “until such a point is reached whereby all operations are transferred to another space within the Palace of Westminster (assumed to be the House of Lords Chamber), to allow the rest of the work to proceed”.

       The project’s sponsor body and delivery authority calculated this scenario could cost between ￡9.5 billion and ￡18.5 billion, taking between 26-43 years.

       A “full decant”of the parliamentary estate, with MPs being housed offsite in a temporary Commons chamber, however, would cost considerable less — between ￡7-￡13 billion — and last between 19-28 years, the report added.

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       The study also found there would be “a number of key risks” associated with a “continued presence scenario”, including fire safety; compliance with health and safety legislation; noise and vibration; lack of provision for a recall of the House of Commons; and changes to parliamentary business, including ways of working and possible changes to parliamentary procedure.

       Garry Graham, deputy general secretary of the Prospect union which represents workers in Parliament, said: “It is clear from the report that a full decant will be cheaper, quicker and safer. From a taxpayers and safety perspective, this is the only credible plan.

       “We cannot allow the faux emotional attachments of some to get in the way of the restoration of the House being achieved safely, expeditiously and in a way that recognises the concerns of staff and achieves value for money for the taxpayer.

       “I am sure that will be fully supported by the new minister for Civil Service efficiency. To come to any other conclusion would be perverse.”