Green’s Dictionary of Slang

(orig. milit.) margarine.

1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 183: Margarine or ‘marge’ is ‘Maggy Anne’.
1982		E. Mac Thomáis Janey Mack, Me Shirt is Black 109: Pat sold everything from bread, Maggie Ryan, butter, [...] candles and pot herbs.
1993		(con. 1910s) W. Woodruff Road to Nab End (2003) 39: Porridge was followed by chunks of home-made bread, covered with Maggy Ann.