THERE is an episode of Blackadder in which our heroes are attempting to sustain two very different gatherings simultaneously under the same roof, so that neither knows of the other’s existence: one, a debauched party for their fellow courtiers; the other, a sombre, puritanical supper for wealthy relatives. The practical demands of such a deceit prove unmanageable; yet, were one to attempt the equivalent online, it would be a doddle. As Helen Lewis recounts in Helen Lewis Has Left the Chat (Radio 4, Wednesday of last week), it is common for people to run multiple lives in parallel via the closed communities enabled by such private social-media platforms as WhatsApp.

The deceits are breathtaking in their audacity, and yet are simple. We hear of a family that maintains two parallel WhatsApp groups, so that the parents can stay in touch with their son’s ex-girlfriend without his knowing. Most horrifying is that of a mother who discovers that there is a group formed of school parents wholly dedicated to complaining about her and her child. Wormholes connecting one group to another are created when a member inadvertently posts to the wrong group, and the existence of parallel realities is revealed.

For all its stupidity, the advantage of X/Twitter is that it is more or less public. Private social networks have no ventilation, and can become hothouses of ignorance and antagonism. Lewis may be over-playing her hand by claiming that this subject offers entirely fresh investigative territory, but her series at least aspires to uncover the ways in which private social networks affect our social, cultural, and political behaviour.

You can’t get much more closed a social network than a monastic order; and the potential dysfunction that arises in such an environment is calmly and clearly unpicked in Book of the Week: Cloistered, the memoir by Catherine Coldstream of her 12 years in a Carmelite convent (Books, 8 March, Feature, 28 March), serialised last week on Radio 4.

If you are looking for an account of religious formation, liturgical practice, or even that thing nebulously referred to as a “faith journey”, then you won’t find it here — at least in this version, edited for radio. What the writer gives us, instead, is a keen sense of the shifting power relationships between the various levels of the convent hierarchy, the office politics of the cloister. It is when two Sisters arrive from another convent that things really start to kick off, “gangs” form, and an election to the position of Mother Superior becomes fraught. It makes one wonder what, had they been allowed them, their WhatsApp groups might have been like.

The World Service is currently broadcasting an outstanding series, co-created with the Canadian Broadcasting Corporation, on the history of the House Un-American Activities Committee. Hollywood Exiles (Wednesdays; full series available on BBC Sounds) is presented by Oona Chaplin, whose grandfather — the great Charlie — himself had a brush with Joseph McCarthy’s monstrous creation. The archive material alone is vivid and disturbing.