Green’s Dictionary of Slang

melt n.3

[SE whore’s melt, ult. milt, roe]

(UK Und.) an unpleasant person.

[UK]N. ‘Razor’ Smith Raiders 182: A runner named Gilbert, a right melt [...] who thought he was a gangster.
[UK]J.J. Connolly Viva La Madness 41: Geezer’s a melt, a one-man crime wave.