Fears are mounting that the £5.6billion costs for restoring Parliament could spiral as details emerged of peers' ideas for their temporary accommodation.
The House of Lords was due to be relocated from the Palace of Westminster to the nearby QEII conference centre with 'minimal' refitting when the huge scheme finally gets under way.
But there is alarm over the scale of the overhaul being proposed to the stopgap building, with peers suggesting a grand new central staircase to bring in more 'natural light', and turning the sixth floor into a catering suite with bars and restaurants.
Changes to the frontage of the conference centre, which is widely regarded as ugly by politicians, are also being mooted.
The ideas were revealed as senior insiders told MailOnline the restoration plan - much of which is essential to fix leaks, fire hazards, asbestos and creaking infrastructure - is already in a 'mess'.
MPs and peers voted two years ago in favour of moving off the estate for the first time since the Luftwaffe bombed chamber in 1941.
Peers have been making plans for their temporary accommodation when the restoration of the Palace of Westminster begins. PIctured is the House of Lords last month
The House of Lords is due to be relocated to the nearby QEII conference centre with 'minimal' refitting when the multi-billion pound scheme finally gets under way
Peers are expected to relocate to the nearby QEII centre during the restoration, while MPs will have a temporary chamber in Richmond House
With costs for restoring the whole Palace of Westminster (pictured) currently estimated at up to £5.6billion, slippage could be catastrophic
There is fury among politicians that they were recently forced to approve a huge rise in the budget for the Big Ben refurbishment - from under £30million originally to around £80million.
With costs for restoring the whole Palace of Westminster currently estimated at up to £5.6billion, anything like the same slippage could be catastrophic.
There is also deep anxiety that the timetable - initially forecast to start in 2025 and end between five and eight years later - will stretch even further.
Complaints have been growing that Opposition members of the ruling Commons commission are trying to add 'all sorts' of upgrades into the proposals. 'The lefties are trying to chuck all sorts in there,' one source said.
MPs are due to sit in a temporary chamber being created in Richmond House, which borders the existing Parliamentary estate. The original scoping report produced by consultants in 2015 laid out a range of possible upgrades to the estate including creating underground meeting space below the current New Palace Yard, with 'natural light from a landscaped courtyard above'.
Commons Leader Jacob Rees-Mogg is understood to be 'all over' the process and constantly reminding colleagues of their responsibility to make sure 'taxpayers get value for money'. Commons Speaker Lindsay Hoyle is also keen to stop the programme running out of control.
Some MPs believe there