Green’s Dictionary of Slang

a sandwich.

1961		Partridge DSUE Supplement.
1980		T. McClenaghan Submariners I ii: There I was lined up for the spam sarnies.
1997		P. Theroux Kowloon Tong 187: Now finish your sarney.
1998		K. Sampson Awaydays 80: I take ages chewing the last morsel of my sarnie.
1999		Observer Mag. 13 June 59: Would you enquire as to whether your bacon sarny might be served with wholemeal bread.
2005		H. Mantel Beyond Black 164: Al would be in the kitchen making a toasted sarnie.
2016		Guardian 2 May 28/1: Pre-prepared sarnie is just pre-posterous.