Hi Peter, There is an entry for Peter Dredge Sr in the 1851 census for Wiltshire, as follows: Dredge PeterHeadWidower77 yearsCarpenter born Hampshire Totten Downer HannahdauMarage 36 yearsborn Britford Wilts Downer Markson-in-law Mar32 yearsDealerborn Charlton Wilts.
This info comes from a relative (a direct descendant of Peter Dredge Jr) who doesn't give the full address from the census.
Peter Dredge was born about 1774 (not 1796).He married Ann White in 1796.Ann was born in 1776 at Odstock Wiltshire and died on 2 Apr 1839.
Their eldest son James was a builder, then schoolmaster then he opened his own school in Salisbury called the Fisherton Academy.He became a Methodist lay preacher and then Assistant Protector of Aborigines.His brother Peter was a carpenter, also lay preacher.James and his family embarked for Australia on the barque "Elizabeth" on 20 March, arriving in Sydney 24 Sept 1838.Peter and his family arrived in Adelaide in Feb 1840 as assisted immigrants.
I have a little more information about Ann White's family, but nothing further back on the Dredges.