The worst loss of civilian life involving a RAF aircraft was 4 Sep 1938.
Audax I K7381, 1 ERFTS, Hatfield
Crashed on houses, Dunholme Road, Edmonton
Sgt Stanley Robert Morris (20) killed (pilot, RAFVR)
Mrs May Lavinia Callaghan (39) died 8.9.38
Doris M Callaghan (16) died 25.9.38
Dennis Callagahan (13) killed
Terence Callagahan (3) killed
John Euesden (45) killed
James Letch (24) died 5.9.38
Edward Letch (20) killed
Benjamin Saunders (43) killed
Mrs Harriet Grace Saunders (37) killed
Roy Saunders (16) killed
Derek Saunders (9) killed
James Alfred Tant (8) killed
Absolutely tragic.
https://aviation-safety.net/wikibase/2421