This week, 12 members of the Extinction Rebellion environmental protest group stripped to their underwear in the House of Commons during another meaningless Brexit debate. They were swiftly arrested on suspicion of “outraging public decency”. But what is decency and what counts as outraging it?

In English law, it is a “plainly indecent act”, visible to two or more people, that is “likely to disgust and annoy”. Most such behaviour is sexual, though the artist Rick Gibson was convicted in 1989 for exhibiting a pair of earrings made from human foetuses. That is pretty disgusting. But are human buttocks equally disgusting in this day and age? If so, the producers of Love Island ought to be nervous.

Decency (Latin decentem, “fitting”) has always been a movable feast. In 2002 and 2003, the “Decent Left” were liberal commentators who wanted to invade Iraq, which in turn outraged other people’s idea of what was decent. Indeed, “decency” once also meant the “decent or orderly condition of civil or social life”. If anyone has been outraging that lately, it’s not those in the public gallery of the House of Commons, but a decent proportion of those sitting below.