 In 1792 , local businessman Joseph Medworth purchased the site of Wisbech Castle , including John Thurloe 's 1660 mansion and the land surrounding it from the See of Ely , building the Georgian Crescent along the bailey walls . As part of his scheme , in 1811 he tried to persuade the Corporation to purchase the mansion and demolish the Old Grammar School building in Ship Street with the intention of building a new street through to the market place . The Corporation refused ( it is usually assumed that the burgesses intended to purchase the mansion for the same purpose after Medworth 's death at a reduced price ) . As a result , in a " fit of pique " , Medworth demolished Thurloe 's mansion and erected the present Wisbech Castle building in 1816 . 
