 Around the time that Harrison was involved in the construction of Skerton Bridge , he received other commissions for work in Lancaster . These included the addition of a clock tower to the Town Hall , the addition of a tower and spire to St John 's Church , and the building of Bridge Houses on the east side of Skerton Bridge . In October 1786 Harrison was asked to prepare plans for substantial improvements to Lancaster Castle ; in January that year he had also won the competition for major improvements to Chester Castle . He worked on both projects simultaneously for the next 30 years , and beyond that until 1815 in Chester , where he added further new buildings . In both projects he designed buildings for prisoners and prison staff , courtrooms and a Shire Hall . Both towns already had gaols , but there was a national move in the later part of the 18th century to improve them , following the campaigns by penal formers led by John Howard . Amongst these reforms were the separation of men and women , and of criminals and debtors , which were incorporated into Harrison 's designs . 
