The dystopian version of England depicted by P. D. James in The Children of Men is a place where the authorities cynically distort language as a way of masking harsh realities. They routinely resort to euphemisms, words and phrases designed to make what is inherently unpleasant sound a little less so.
Euphemisms are quite common in everyday speech. For instance, when a family pet dies, it's not uncommon to hear a sensitive parent try to make their children feel a little better by saying that the poor unfortunate creature in question has crossed the Rainbow Bridge to heaven.
Such euphemisms are quite harmless, but it is possible to resort to euphemistic language that has more sinister intent. We see many such examples in The Children of Men. First and foremost, we have a dictator, Xan Lyppiatt, referred to by the official title of Warden of England.
This title makes him sound like he's the protector of the English people, that he's there to keep them safe from harm. In actual fact, however, he's a cruel despot presiding over an evil system of government. What we can observe here is a classic case of a euphemism being put to sinister use, namely to cloak the truth with an entirely false picture of reality.
Much the same process is in evidence with regard to the Quietus. To some people, this might sound like the name of a choir or a classical music record label. At the very least, it has a very pleasant ring to it, not least because it contains the word “quiet.”
But once again, we're dealing with another highly sinister euphemism. For the Quietus is actually a public ceremony in which the elderly are encouraged by the state to kill themselves so as not to be a burden to an aging population.
Just as Xan Lyppiatt will never refer to himself as a dictator, so the Quietus will never be referred to as a suicide ritual. This is because, in the dystopian society depicted in The Children of Men, language has been divorced from reality.