The cost estimate for the restoration and renewal (R&R) programme, including the restoration of the Palace and temporary accommodation for the House of Lords, will be determined as part of an outline business case (OBC), which is being prepared by the R&R Sponsor Body. The OBC is being developed in line with the resolutions agreed by both Houses in early 2018, which endorsed the Joint Committee on the Palace of Westminster's recommendation that a full and timely decant of the Palace was the best and the most cost-effective delivery option.
In June 2015 the Independent Options Assessment (IOA) was published. It was produced by a Deloitte-led consortium in 2015, and was then considered by the Joint Committee on the Palace of Westminster which published its report in 2016. Both these events predated the establishment of the shadow Sponsor Body in September 2018. For full decant, the IOA estimated indicative costs for comparative purposes at between £3.52 billion and £3.87 billion, and assumed a construction start date of 2020. It cautioned that no budget could be set until a detailed design brief and means of delivery were agreed, and that these figures should not be taken as setting or estimating a budget for the Restoration and Renewal Programme. The IOA was not intended to provide fully costed estimates for the programme as they would be contingent upon full surveys, inspections, designs and the agreement of requirements. To provide these is the purpose of the shadow Sponsor Body's outline business case.
Once the programme's scope, requirements and forecast benefits have been determined the proposed approach to the works, including a funding envelope and schedule, will be put before both Houses for decision in 2022 as required by section 7 of the Parliamentary Buildings (Restoration and Renewal) Act 2019. Throughout the development of the OBC there will be a rigorous review of all options and costs, in line with best practice established by the Infrastructure and Projects Authority and external reviews by the National Audit Office.