John Peel, n. — Green’s Dictionary of Slang

John Peel n.

[? 18C ballad, with lines ‘D'ye ken John Peel with his coat so gay' and ironic use of ‘We'll follow John Peel through fair and through foul / If we want a good hunt in the morning’]

(UK Und.) a relatively well-off individual, targeted for a theft or swindle.

1926

Portsmouth Eve. News 23 Nov. 4/4: A man with [...] only £1 or £2 is a ‘case phunt’ or a ‘deuce phunt’. If he has £5 he is a ‘flim’. £10 an ‘Uncle Ben’, and more than that a ‘John Peel’ or a ‘Sarker’.