Repair costs for the Elizabeth Tower in the Palace of Westminster have now doubled to an estimated £61 million, parliamentary authorities have said.
The conservation project for the clock tower, which houses the bell known as Big Ben, was originally priced at £29 million in the spring of 2016.
The repair effort caused controversy when it was announced that Big Ben would only chime on special occasions over the next four years while the works were being carried out.
The House of Commons and House of Lords Commissions have been told that the increase in costs is due to a better understanding of the complexity of the work needed to restore the tower.
A spokeswoman for the House of Commons said: "The commissions expressed their disappointment in the cost increases, and the unreliability of the original estimate.
"They instructed officials to provide regular updates on progress and costs to the relevant domestic committees so they can keep the commissions fully informed of the project.
"They also reiterated their commitment to preserve the Elizabeth Tower and Great Clock for future generations."
In a joint statement the clerk of the House of Commons, the clerk of the Parliaments and the director general of the House of Commons, said: "We acknowledge that there have been estimating failures and we understand the concern of the commissions.
"In advance of tendering contracts, the initial high level estimates were set at a lower level to avoid cost escalation from the market.
"Subsequent estimates, using better data and more extensive surveys, better reflect the true likelihood of the costs.
"We believe that we now have a more accurate estimate of the cost of the works and will report regularly to the committees on the progress of work."