Green’s Dictionary of Slang

flagellation, only when used in a sexual context.

1959		F. Norman in Encounter n.d. in Norman’s London (1969) 64: I don’t care what you do as long as you don’t get on my beat, because I’ve only had three short times tonight, and one of them was a flage merchant.
1967		G. Freeman Undergrowth of Lit. (1969) 79: Customer to Proprietor: ‘Got any straight sex, then?’ Proprietor, apologetically: ‘Sorry mate, it’s all got a bit of fladge in it.’.
1972		Times Literary Supplement 4 Aug. 916: The two big bookstalls in Trastevere go in for porn and fladge.
1986–7		Maledicta IX 167: In England flage[llation] has long been a staple of pornography.
1989		J. Morton Lowspeak 59: Fladge and padge – flagellation and pageantry. Bondage and dressing up for sexual titillation.
1997		(con. 1960s) A. Frewin London Blues 69: flage is flagellation and sado-masochistic material.
1997		Deviants’ Dict. 🌐 Why use the term ‘flagellation’, which for many people has overtones either of religion or the ‘kinky’ 1960s with its ‘fladge’?
2006		in D. Seabrook Jack of Jumps (2007) 202: Malik specialized in [...] ‘corrective treatment for men’, so maybe Fleming was trying her hand at fladge.
2020		‘Nick Urzdown’ in Wickstead Soho Typescripts: 14: ‘The stories in the typescripts always followed a theme be it straight sex - always called shaggers in the trade, or fladge - flagellation - which is the trade name for spanking’.
2020		Wickstead Soho Typescripts: 16: : ‘The trade had its own private language [...] Bondage and flagellatory material was “bond” and “flag”’ .