Green’s Dictionary of Slang

lavatory; also attrib.; thus lav paper, lavatory roll.

1913		C. Mackenzie Sinister Street I 99: Tell the army to line up behind the lav. at four o’clock.
1934		S. Beckett More Pricks than Kicks 119: I’ll take mine to the lav, I don’t feel very well.
1947		J. Maclaren-Ross ‘The Dark Diceman’ in Bitten by the Tarantula (2005) 208: The stairs that led down to the [...] gents lav.
1954		J. Phelan Tramp at Anchor 185: Working out sums on bits of lav. paper.
1959		W. Hall Long and the Short and the Tall Act II: That was the most expensive trot to the lav I ever had, I know that.
1960		K. Williams Diaries 11 Jan. 159: Went after a flat in St James St. Unfortunately no bathroom or lav.
1971		N. Smith Gumshoe (1998) 69: I was nervous that night all right [...] I went to the lav about nine or ten times.
1981		S. Berkoff Decadence in Decadence and Other Plays (1985) 26: The next thing then you will espy is the lav staring you in the eye.
1985		B. Robinson Aussie Bull 21: Another wit insists on using a marker pen to put a black cross on the arm of a mate who’s going to the lav.
1991		Reeves & Mortimer Vic Reeves Big Night Out n.p.: He waved goodbye as he sank out of sight like a crab in a workman’s lavy.
2005		(ref. to 1950s) A. Bennett Untold Stories (2006) 67: The outside lav and the sheaf of newspapers hung behind the lave door.
2014		H. Mantel Assassination of Thatcher 224: Bugger this, where’s the lav?
2017		G. Gilmore Headland [ebook] He made an excuse about needing the lav.