Green’s Dictionary of Slang

1. a magistrate.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1935		A.J. Pollock Und. Speaks.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3.
1969		S.T. Kendall Up the Frog.
1971		J. Jones Rhy. Cockney Sl.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.

2. (bingo) the number eight.

1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.
2001		J. Burkardt ‘The Bingo Code’ Wordplay 🌐 8: garden gate.
2003		Guardian G2 8 May 4: Several of the company’s planned substitutions betoken innocence lost. ‘The garden gate, number eight’ will become the imperfectly rhyming ‘Gareth Gates’.

3. £8.

1989

in G. Tremlett Little Legs 194: garden £8.

4. a friend [= mate n. (1)].

2002

B. Kirkpatrick Wicked Cockney Rhy. Sl.