Green’s Dictionary of Slang

long-tailed beggar n.

1. a cat [the supposed story of a sailor who came home after his first voyage unable to remember the name of a cat and asked his mother ‘What’s she called, that ’ere long-tailed beggar?’].

[[UK]Marryat Peter Simple (1911) 10: You must larn to chaw baccy, drink grog, and call the cat a beggar].
[UK]Hotten Sl. Dict.
[UK]Sl. Dict.

2. a large denomination sterling note [long-tailed ’un n.].

[UK]J. Manchon Le Slang.