Besides historical studies on the Roman Empire and on the early history of Great Britain he was a reviewer for London magazines and a poet.
Whitaker's views on early British society were idiosyncratic: in his History of Manchester, (1771–75) he argued that the ancient Britons had already established a feudal system, and under the Romans had been entirely converted to Christianity (his erudition was recognised as remarkable but the theories were mostly illfounded).
[citation needed] The Life of St Neot, published posthumously in 1809, was similarly intended to challenge traditional orthodoxies in the form of the extant saint's lives.
He died at his rectory on 30 October 1808 and was buried in Ruan Lanihorne in Cornwall; his widow Jane (née Tregenna), who had long suffered ill health, lived on until 30 December 1828.
He studied the decline of the Cornish language and concluded in his work The Ancient Cathedral of Cornwall[3] His numerous writings are listed in Bibliotheca Cornubiensis by Boase and Courtney and in Palatine Note-book, vol.