If MP and peers were moved out for six years, the cost would drop to £3.5bn, the BBC has reported.

The 150-year-old Grade I listed building is partly sinking, contains asbestos and has outdated cabling.

A 2012 report warned the building could suffer “major, irreversible damage” without significant restoration work.

The Commons and Lords will have to vote in the next few years on what to do.

The £3.5bn option would include some new features, such as a lift up the Elizabeth Tower, which with its famous clock and bell is popularly known as Big Ben, a media centre for TV interviews and “increased breakout, formal and informal meeting areas” for those who work in the Palace of Westminster.

For a slightly higher spend of an estimated £3.9bn, the full move-out of MPs and peers would also enable a new visitor centre, including exhibition, education and conference facilities.

The Independent Options Appraisal report also has two halfway-house options, which would see a partial vacation of Parliament - with the Commons going first, followed by the Lords.

That would cover a total time period of between nine and 14 years, but would most likely last 11 years.

Under that proposal, basic repairs - such as improving fire safety, removing asbestos and restoring damaged stonework - would cost an estimated £3.9bn.

A higher-spec version of the partial move-out, with some of the same extras as a full move-out, would cost an estimated £4.4bn.

The highest conceivable cost, the report said, would be £7.1bn. This assumes maximum risk and inflation levels and applies to the most expensive of the options put forward.

The report’s summary says that it does not seek to advise Parliamentary authorities which option to choose, but concludes “a full move out is described as providing the best opportunity to mitigate risks, but the report recognises this would create logistical challenges”.

If MPs and peers choose not to move out at all, the work is projected to last between 25 and 40 years, although it is suggested 32 years would be the most likely duration.