MPs may have to ask permission from the Queen before a costly refurbishment of Parliament goes ahead.
The House of Commons and House of Lords are preparing to “decant” to another location while essential repairs to the Palace of Westminster are carried out.
MPs voted to allow the move to go ahead last month, but the government had admitted the ambitious project may not be able to get underway without the royal nod.
In response to a written question from prominent historian and cross-bench peer Peter Hennessy, former chief whip Lord Young said: “As a parliamentary programme, the delivery of the Restoration and Renewal (R&R) of the Palace of Westminster is a matter for both Houses of Parliament.
“I understand that the Queen’s consent may have to be sought in relation to the bill to be brought forward in respect of R&R.”
But officials are not expecting a hitch. A project spokersperson told HuffPost UK: “Any bill which affects the prerogative, hereditary revenues, personal property or interests of the Crown requires Queen’s Consent in both Houses before it is passed.
“Queen’s Consent is usually required for several bills each year.”
A date for the move has not yet been set, but is is expected the Commons would move to Richmond House, on nearby Whitehall, and the Lords would relocate to the Queen Elizabeth II conference centre.
A formal body is expected to be set up to provide up-to-date costings of the work - which could be as much as £3.5bn - and a “realistic” timetable for the restoration.
The UNESCO World Heritage Site is partly sinking, contains asbestos and has outdated cabling, with a 2012 report warning it could suffer “major, irreversible damage” if its problems were not tackled.