It would be "imprudent" for MPs to commit to the restoration of parliament that could cost up to £4bn, without more work being carried out into "the hugely expensive project", the Treasury Select Committee warned today.
The Committee has launched an inquiry into the project which will cost between £3.5bn and £4bn, if carried out over the minimum period of five to eight years, according to consultants.
In its preliminary report today, said that work by Deloitte and an investigation by the Joint Committee on the Palace of Westminster, while thorough, was not sufficient and neither "constitutes a business case".
The business case is not expected to be available until around January 2019.
Andrew Tyrie, chair of the Treasury Committee, said: "This is one of the largest major restorations in the history of the public sector. Apparently, it is likely to cost at least £3.5bn over five to eight years. This can only be justified to taxpayers if parliament and the public see the evidence required to make an informed decision."
The Committee's inquiry will "challenge and assess" the work of the existing reports and it will hold oral sessions to go through written evidence supplied to the Committee.
Until such work has been carried out, it would be imprudent for parliament to commit to a specific option.
That's despite a recent report from the Public Accounts Committee recommending MPs leave the building urgently as "the risk of catastrophic failure is high and growing with every month that passes".
The Treasury Committee said it will examine how serious the risks are and how rapidly they are increasing.
It said the inquiry will likely be relatively short and specific, but that given the "enormous sum" involved, it is vital the case for spending and cost-effectiveness are thoroughly scrutinised and plans rigorously challenged.
The current plan is for a "full decant of the entire building", with the House of Commons acquiring Richmond House and creating a temporary chamber in the courtyard there.
The Committee wants to assess the merits of the other options and offer "constructive challenge" to the case for proceeding imminently with the preferred plan.