Green’s Dictionary of Slang

potted head adj.

dead.

1993		I. Welsh Trainspotting 99: Granty . . . ye didnae hear? [...] Deid, Potted heid.
2002		B. Kirkpatrick Wicked Cockney Rhy. Sl.
2012		(con. 1980s) I. Welsh Skagboys 496: The perr auld boy was found potted heid in his flat.
2018		I. Welsh Dead Man’s Trousers 158: The Brian Jones cat that’s potted heid.