<P> In 1839 Charles Barry toured Britain, looking at quarries and buildings, with a committee which included two leading geologists and a stonecarver . They selected Anston, a sand - coloured magnesian limestone quarried in the villages of Anston, South Yorkshire and Mansfield Woodhouse, Nottinghamshire . Two quarries were chosen from a list of 102, with the majority of the stone coming from the former . A crucial consideration was transportation, achieved on water via the Chesterfield Canal, the North Sea, and the rivers Trent and Thames . Furthermore, Anston was cheaper, and "could be supplied in blocks up to four feet thick and lent itself to elaborate carving ." </P> <P> Barry's New Palace of Westminster was rebuilt using the sandy - coloured Anston limestone . However, the stone soon began to decay due to pollution and the poor quality of some of the stone used . Although such defects were clear as early as 1849, nothing was done for the remainder of the 19th century even after much studying . During the 1910s, however, it became clear that some of the stonework had to be replaced . In 1928 it was deemed necessary to use Clipsham stone, a honey - coloured limestone from Rutland, to replace the decayed Anston . The project began in the 1930s but was halted by the outbreak of the Second World War, and completed only during the 1950s . By the 1960s pollution had again begun to take its toll . A stone conservation and restoration programme to the external elevations and towers began in 1981, and ended in 1994 . </P> <P> As of October 2012, the north wall of Westminster Hall is undergoing restoration . The restoration of the inner courtyards is also ongoing . As of April 2012, four have been completed, including the two largest (Speaker's Court and Royal Court); the rest are scheduled to be completed by October 2016 . </P> <P> The Palace of Westminster features three main towers . Of these, the largest and tallest is 98.5 - metre (323 ft) Victoria Tower, which occupies the south - western corner of the Palace . Originally named "The King's Tower" because the fire of 1834 which destroyed the old Palace of Westminster occurred during the reign of King William IV, the tower was an integral part of Barry's original design, of which he intended it to be the most memorable element . The architect conceived the great square tower as the keep of a legislative "castle" (echoing his selection of the portcullis as his identifying mark in the planning competition), and used it as the royal entrance to the Palace and as a fireproof repository for the archives of Parliament . Victoria Tower was re-designed several times, and its height increased progressively; upon its completion in 1858, it was the tallest secular building in the world . </P>

Who was prime minister when the houses of parliament opened