Telegraph (UK) 26 Sep 2010
Despite surviving from Roman times, the humour no longer considered acceptable, according to officials at the London Borough of Barnet. The edict was issued in a 12-page booklet entitled Cultural awareness: General Problemswhich came to light through a Freedom of Information request. It states: “Humour can be incredibly culture-specific, and is very open to misinterpretation or even offense [sic] by other cultures. And don’t forget when you don’t know what people are laughing at, it is very easy to imagine that they are laughing at you.” The guide adds: “British mother-in-law jokes, as well as offensively sexist in their own right, can also be seen as offensive on the grounds that they disrespect elders or parents.”
http://www.telegraph.co.uk/news/newstopics/howaboutthat/8026003/Council-outlaws-mother-in-law-jokes.html