Ah, parliament, with its magnificent conventions, where you are allowed to honk like a goose on fire while someone is speaking, can say “misspoke” but not “lied”, and can enjoy round-the-clock access to snuff from the House of Commons doorkeeper, but are not allowed to remain in bed when you have just had a baby. On paper, an MP can take maternity leave, regardless of whatever constitutional crisis is unfolding, thanks to “pairing”, where a counterpart will be found to cancel out your absence by not voting themselves. It is known as a “gentleman’s agreement”, which is a technical term, meaning: “It will be honoured until it actually matters, then it’s gloves off, suckers.” There should be a code for when you save your noblest, most altruistic behaviour for when it counts, and we could call that a lady’s agreement.

On Tuesday, Brandon Lewis, Conservative party chairman, was paired with Jo Swinson, deputy leader of the Lib Dems, who has a three-week-old baby. The non-voting pact was remembered all the way through the day, until it came to two Brexit amendment votes at the end, when he voted with the government to save it from what might otherwise have been a general-election-triggering defeat. The whips have taken the blame. Fair enough: it was late, people get tired, it’s easy to make an “honest mistake”, if by that you mean: “I honestly and mistakenly thought nobody would notice, since she’s a Lib Dem anyway, and a woman to boot.”

Four Labour MPs committed their own acts of betrayal by voting with the government to keep this catastrophic show on the road, but we will have to leave them for another day. A further two Labour MPs were also paired for maternity leave, Laura Pidcock and Cat Smith – those pairings were both honoured. This is because Labour babies are cuter than Lib Dem babies. Look, I don’t make the rules.

You could make the case that there is no endemic sexism here, since men have faced pairing crises in worse circumstances. For example, in 1979, when the terminally ill Sir Alfred Broughton was almost brought to the Commons in an ambulance for a vote of no confidence against the then Labour prime minister James Callaghan. The government collapsed and Broughton died five days later. The great pairing scandals of the 70s, though, are mainly remembered not for the ambulances drawing up to parliament, but for Michael Heseltine grabbing the mace and swinging it about, in another charming parliamentary custom where the mace stands in for anything else an honourable member might want to swing.

The troubling arrival of potentially childbearing MPs in representative democracy has raised questions about how hospitable the Commons is to women. The fresh wind of modernity brought with it reasonable objections, such as: “Why can’t I breastfeed in here, when you’re allowed to swing a mace?” Brexit, however, has always been a throwback male affair. The women involved – even the PM – look less like colleagues, and more like hostages in a roid-rage event. But this has surely hit its hard limit: to cheat a woman with a new baby is elementally unjust, signalling total rottenness from the inside out. There is no fit penance for Lewis, but I like the idea of making him give all his votes, in perpetuity, to baby Gabriel Swinson, who will choose, by giving some baby signal, which way he wants Lewis to vote.

What price nuclear power? Its cost could be what finally persuades us to ditch it

Nuclear power has hit what might be its derailing pothole: it is not as cheap as renewable energy. The National Infrastructure Commission came back with this conclusion as tactfully as it could, as if trying to put nuclear in a care home without upsetting it: it’s not that there’s anything wrong with new nuclear power stations. It is just that they won’t be on stream until the 2030s, while solar and wind are already so good, improving so fast, that should we not … could we not consider just doing that?

The campaign against this energy source started in parallel with that for disarmament in the 1970s and 80s: stickers with a big, smiling sun saying “Nuclear Power? No Thanks!” The underlying message was: “Why not use the sun instead?”, a hippy pipe-dream that, inconveniently for the massed forces of anti-hippy, turned out to be very sensible. There was also the risk of nuclear accident, which could wreak devastation undreamed of even by people who killed things on purpose. This, too, came to pass, although it has taken the 30-plus years since Chernobyl, still in a 30km exclusion zone, to digest this as fact. There were anxieties about waste management and the ambient discharge of radioactivity, none of which was ever allayed, and more recently, a soft-nationalist argument that if we had to build nuclear power plants, we should do it ourselves and not hand it to the French and Chinese.

In short, every argument – patriotic, scientific, ecological and humanitarian – has been levelled against nuclear power, yet the only dart to scratch its resilient hide is that it is perhaps not as cheap as it at first appeared.

It is inevitable that it would take this long, if we only value what we can count. But there are loads of things that we evaluate by criteria other than money: relationships; art; tomatoes. We shouldn’t have to wait until “best” coincides with “cheapest”.

Warning: man eats shark

A 9ft blue shark has been spotted close to the shore at St Ives, in Cornwall, but is it really blue, or is that just the beautiful light? Never mind the grace and majesty, for the time being, swimmers are being forcefully advised not to get into the water with the Prionace glauca. They should be warning the shark: this is the most dangerous place in the country, maybe even the world, to be high-density, high-protein edible marine life. Someone’s probably making a romesco sauce as we speak, and writing a complicated price per kilo on a chalkboard.

• This article was amended on 23 July 2018. An earlier version said Sir Alfred Broughton “was stiffed by his Tory opposite, Bernard Weatherill, in a vote of no confidence”. In fact Weatherill, the Conservative deputy chief whip, in discussions with Walter Harrison, Labour’s deputy chief whip, did agree to a pairing arrangement that would have obviated bringing Broughton to the Commons for the vote. But Harrison then decided not to hold Weatherill to the agreement.