MPs are warning that the Palace of Westminster is in danger of a "catastrophic failure" unless ministers bring forward a major renovation programme as a matter of urgency.
The Commons Public Accounts Committee (PAC) has backed a plan for a "full decant" of the building - home to the Houses of Parliament.
MPs and peers would move out for a period of around six years while the work is carried out at an estimated cost of £3.5 to £3.9 billion.
The committee said the proposal put forward last year by a joint committee of the Commons and the Lords represented the "most economical, effective and efficient" option for restoring the palace to a proper state.
As a Unesco world heritage site, the committee stressed that ultimate responsibility for taking action lay with the Treasury while further "delay and indecision" would simply add to the final cost.
"This internationally-recognised building is in a state of extreme disrepair. The risk of a catastrophic failure is high and growing with every month that passes," it said.
"It must be repaired. For a world heritage site that is the home of the 'mother of parliaments', doing nothing is not an option.
"The best value for money will be achieved by getting on with it. The Government should not delay any further in putting the proposal for a decision in principle before both Houses."
The position however is complicated by the decision of another committee of MPs - the Commons Treasury Committee - to conduct its own inquiry into the renovation plan.
Launching the inquiry in January, the committee chairman Andrew Tyrie said the original joint committee proposal and the consultants' report on which it was based did not provide sufficient evidence to make even a "preliminary decision" on the way forward.
But with the Treasury Committee yet to begin hearings on the issue, PAC chairman Meg Hillier warned they could not afford further hold-ups.
"Delaying a decision on how that work should be carried out will only add to the costs and risks," she said.
"The longer the House of Commons spends mulling new or alternative options, the greater the chance that public money is wasted."