<P> The worst raid took place in the night of 10 / 11 May 1941, when the Palace took at least twelve hits and three people (two policemen and the Resident Superintendent of the House of Lords, Edward Elliott) were killed . An incendiary bomb hit the chamber of the House of Commons and set it on fire; another set the roof of Westminster Hall alight . The firefighters could not save both, and a decision was taken to try to rescue the Hall . In this they were successful; the abandoned Commons Chamber, on the other hand, was destroyed, as was the Members' Lobby . A bomb also struck the Lords Chamber, but went through the floor without exploding . The Clock Tower took a hit by a small bomb or anti-aircraft shell at the eaves of the roof, suffering much damage there . All the glass on the south dial was blown out, but the hands and bells were not affected, and the Great Clock continued to keep time accurately . </P> <P> Following the destruction of the Commons Chamber, the Lords offered their own debating chamber for the use of the Commons; for their own sittings the Queen's Robing Room was converted into a makeshift chamber . The Commons Chamber was rebuilt after the war under the architect Sir Giles Gilbert Scott, in a simplified version of the old chamber's style . The work was undertaken by John Mowlem & Co., and construction lasted until 1950, when King George VI opened the new chamber in a ceremony which took place in Westminster Hall on 26 October . The Lords Chamber was then renovated over the ensuing months; the Lords re-occupied it in May 1951 . </P> <P> As the need for office space in the Palace increased, Parliament acquired office space in the nearby Norman Shaw Building in 1975, and in the custom - built Portcullis House, completed in 2000 . This increase has enabled all MPs to have their own office facilities . </P> <P> The Palace of Westminster, which is a Grade 1 listed building, is in urgent need of extensive restoration to its fabric . A 2012 pre feasibility report set out several options, including the possibility of parliament moving to other premises while work is carried out, also at this time the option of moving Parliament to another new build location was discounted for the preference of staying at the Westminster site . An Independent Options Appraisal Report released in June 2015 found that the cost to restore the Palace of Westminster could cost as much as £ 7.1 billion if MPs remain at the Palace whilst works take place . MPs decided in 2016 to vacate the building for six years starting in 2022 . </P>

Who was the prime minister when the houses of parliament opened