Hewetson was born in Birmingham to a wealthy family and was educated at Shrewsbury School before studying medicine at Magdalen College, the University of Oxford.

[2] In the run up to the Second War World he became active in the Forward Movement of the Peace Pledge Union with his companion Peta Edsall.

[1][2] In 1940 Hewetson was imprisoned for a week for selling a "working class paper" outside Hyde Park having refused to pay a £1 fine.

[6] In 1945, alongside fellow War Commentary contributors Vernon Richards and Philip Sansom, Hewetson was sentenced to nine months imprisonment for conspiring to cause disaffection among members of the armed forces under Defence Regulation 39a.

Following lobbying by Dr Charles Wortham Brook and MP Rhys Davies (both unknown to Hewetson) he was released early, on the 12 September 1945, on the condition that he work full time in a hospital.