The three diaries of John Knyveton (1729-1809) were published between 1937 and 1946. They purported to have been the journals of someone who served as a naval surgeon during the Seven Years War and later became a man-midwife in London, edited and annotated by Ernest A. Gray. The diaries contain factual, historical and linguistic inaccuracies which indicate that they were written after the events described, and are based on the life of Thomas Denman (1733-1815). In this article we describe the errors in the diaries and review the life and work of Ernest A. Gray who seems to have been the real author. Many publications have quoted from the diaries, the writers being apparently unaware of the semi-fictitious nature of the diaries. We give recent examples of them being cited in historical studies. This paper is intended to make their unreliability as a historical source more widely known.