Restoring parliament without a full decant of MPs could take up to 76 years, while the bill for repairs would stretch to £22bn, a new report by the body set up to investigate how the project should be handled has found. MPs, peers and senior parliamentary officials are still split on the best way to proceed with extensive works to the Victorian building given safety concerns about crumbling masonry, the lack of protection against flooding and decades-old electrical wiring. Under the most recent plan, MPs were expected to move to Richmond House, the former home of the Department of Health, while the Palace of Westminster – with a floor plate the size of 16 football pitches and containing 1,100 rooms, 100 staircases and 3 miles of passageways – is being restored. However, the idea was abandoned last year. Alternatives were drawn up and presented to the House of Commons Commission, which were released on Wednesday. The cheapest plan involved a full decant of the Palace of Westminster, for between 12 and 20 years, with the work costing in the region of £7bn to £13bn. With MPs elsewhere for much of the time, the report estimated the works would take between 19 and 28 years. If MPs maintained a “continued presence” in the palace, where “all essential and highly desirable functions could be accommodated but in more condensed space”, the report found that the work would cost more and take longer. In one scenario, 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”. It estimated this would increase restoration costs to between £9.5bn and £18.5bn, taking 26 to 43 years. And in a third possible scenario, which would cost the most and take the longest, business would remain within the chamber “throughout the entirety of the restoration and renewal programme of works” with “no transfer”. It is estimated this would cost between £11bn and £22bn and take in the region of 46 to 76 years. This was conditional on recess being extended to scrap the three-week return for MPs between their summer and party conference breaks, so that there was no parliamentary business for four months, from mid-July to mid-October. The figures do not take into account inflation, meaning the true cost over several decades would likely be billions more expensive, given compound interest. The report was not well received by the Commons Commission, and led to it voting last month to bring the sponsor body for the works in-house. One of the plans being considered by senior Commons officials is to use boats to deliver materials and remove detritus via the River Thames. This would help minimise disruption around Westminster, but also make it harder for MPs, peers and their staff to operate as normal on the current site. Garry Graham, deputy general secretary of the union Prospect, said a full decant was “the only credible plan”, and would be cheaper, quicker and safer. He added: “We cannot allow the faux emotional attachments of some to get in the way of the restoration off 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.”