Are you sure that this the same David Halket? In the 1858 Northumberland Directory there is a David Halket at 9, Eldon Street, Newcastle. In the Directories for Liverpool 1825-1827-1829 there is a David Halket, timber merchant, also in 1825 surveyor for shipping, at 35 Grafton Street, Liverpool. In the London Directories for 1841 and 1852 there is another David Halket, (born 1793 in Scotland) insurance broker, shipping and general agent at 19 St. Helens Place, he is also in the 1851 Census with his family at St. Helen Middlesex. There are also three David Halkets in the 1841 census for Scotland. Regards Stan Mapstone