Green’s Dictionary of Slang

1. the number four.

1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 411/2: There’s people there talk backward – for one they say eno [...] for four ruof.
1885		Edinburgh Eve. News 26 Dec. 3/5: ‘Eno’ is one; ‘owt,’ two; ‘eerth,’ three; ‘rouaf,’ four; ‘exif,’ five; and ‘xis’ pronounced exes, six.
1953		J. Franklyn Cockney 297: Rouf (four).
1977		D. Powis Signs of Crime 199: Rouf Four (London backslang).
1989		(con. 1950s–60s) in G. Tremlett Little Legs 196: roaf £4 and sometimes £40 (probably deriving from the racecourse trick of spelling words backwards; it is similar to four spelt thus, but pronounced roaf as in loaf).

2. 4 pence; 4 shillings.

1950		Eve. Teleg. (Dundee) 4 Sept. 5: The costers have their own money-slang [...] 4d a ‘rouf’’.
1984		Partridge DSUE (8th edn) 990/1: ca. 1945–70.

3. £4, £400.

1959		F. Norman in Encounter n.d. in Norman’s London (1969) 61: four pounds – Rouf.
1976		(ref. to 1930s–70s) R. Barnes Coronation Cups and Jam Jars 207: Rouf – £4.

4. a four-year prison term etc.

1958		F. Norman Bang To Rights 138: That was it I got a rouf.
1979		F. Norman Too Many Crooks Spoil the Caper 77: ’E done eighteen moon out of a rouf an’ got out on parole.