The world's biggest architecture firm has proposed moving the UK's Lords and MPs into a bubble-like building on London's River Thames to reduce the cost of refurbishing the crumbling Palace of Westminster.

It is estimated that it could cost up to £7bn to revamp the Houses of Parliament.

Gensler, which has one of its largest offices in London, wants to create a 250-metre-long and 42-metre-deep temporary parliament building from steel modules and a wooden frame clad in curved panels of glass.

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The modules would be made by British shipbuilders before being transported along the River Thames and assembled on steel platforms behind the neo-gothic Palace of Westminster.

The floating building would be shaped like an elongated bubble, and separated into two areas internally – one for the House of Commons and one for the House of Lords. These would be expressed externally by two gentle bumps at either end of the structure.

Gensler's concept is based on the hammer-beam roof of Westminster Hall, the roof of the Palace's oldest building, which is the largest medieval timber roof in Europe and was commissioned in 1393 by Richard II.

Gensler has proposed creating a 250-metre-long and 42-metre-deep temporary Parliament on the River Thames.

A spokesman said: "The building would be a dramatic, hi-tech, wooden-framed structure covering 8,600 square metres, which would provide all the necessary environmental and acoustic containment.

"The structure would add a new iconic landmark to London and would not impact the protected vista of the Palace of Westminster from the summit of Parliament Hill."

Built between 1840 and 1870, the Palace of Westminster – also known as the Houses of Parliament – was designed by Charles Barry and Augustus Pugin. It contains the remnants of much older structures that date back to the 1000s.

It is now in urgent need of refurbishment work estimated to cost between £4 billion and £7bn.

MPs and Lords will be relocated for at least six years to enable the project.

Gensler said its proposal would cost around £160m, representing a £1.8bn saving in decanting and rental costs, and could be relocated for use elsewhere once the refurbishment work was complete.