The £7bn refurbishment of Parliament will be delayed by between one and three years, MPs and peers working on the project have told The Independent on Sunday.

Work had been pencilled in to start in mid-2020, but members of the cross-party restoration and renewal committee think this is too ambitious, given the amount of preparation work that will be needed.

Parts of the Palace of Westminster need to be better surveyed ahead of such a major revamp, while it will also take time to decant parliamentarians and their staff to other parts of the Parliamentary estate. For example, better mapping of the foundations is needed – the palace was built on marshland – and a small building next to the Department of Health in Whitehall might have to be knocked down to make way for an as yet uncosted temporary chamber.

A separate set of works to bring the neighbouring Northern Estate, which is crammed with crumbling listed buildings, also needs to be completed before the main refurbishment takes place. But this work has not yet started and is already behind schedule.

‘MPs and peers will leave for six years, rather than have builders work round them’ (AFP/Getty)

A senior MP said: “They really need to get the Northern Estate finished before restoration and renewal because it’s a big part of the jigsaw. We will be relying heavily on the Northern Estate to accommodate extra offices and facilities.”

Sources on the committee also said there was a growing hope that the palace could get its makeover for far less than the £4bn to £7bn calculated by a team led by Deloitte Real Estate last year. There are even suggestions it could be as low as £1bn, a more palatable figure for the public, although many think this is not achievable.

One of the reasons committee members think it could come in under budget is that the work could be made exempt from VAT. They think it is silly to charge the levy, given that it will be state money that would go back to the Treasury.

The committee, which includes the Commons leader Chris Grayling, will finalise its plans in the coming months. There is agreement that MPs and peers will have to move out of the palace for about six years rather than take the longer, more expensive option of having contractors work around them.