Green’s Dictionary of Slang

to have sexual intercourse; thus furgler/fergler, furgling n.

1923		in E. Cray Erotic Muse (1992) 230: They fergie [sic] a bull and fill him full / those hardy sons of bitches.
1947		C. Willingham End as a Man (1952) 83: A natural-born fergler.
1966		(con. 1948–52) L. Thomas Virgin Soldiers 21: A harmless mechanic [...] quietly furgling another WRAC in the long elephant grass at the side of the garrison road.
1970		Current Sl. V:3 6: Flurgle, v. To have sexual intercourse.
1988		Sundey Morn. Herald 24 Sept. 3/6: ‘It seems to signal to other males something like: “I’m not going to fight you or be aggressive but, in brackets, if you turn your back I’ll furgle your wife”’ [Simes:DLSS].
1988		Sundey Morn. Herald 24 Sept. 3/6: Spring is in the air and the young wrens’ fancy turns to ‘furgling’ [Simes:DLSS].