Don’t worry, this isn’t a piece about fishing quotas. It’s about the word ‘mackerel’ itself. Specifically, the fact that St John’s Wood is the only London Underground station to share no letters with it.

Really? Half a page in The Spectator, just about that? Well, yes. The fact has gathered a life all of its own. It’s been doing the rounds in pub quizzes for ages. At least 20 years: in a trailer for his 1999 TV chat show, Jeremy Clarkson promised to reveal the answer (and then didn’t). No less an authority than Only Connect host Victoria Coren Mitchell calls it her favourite quiz question ever. ‘It’s the comic juxtaposition,’ she explains. ‘Putting a funny word like “mackerel” next to a grand, elegant place like St  John’s Wood.’ Note that ‘St’, by the way. That’s how it’s spelled on the Tube map: if it were ‘Saint’ the fact wouldn’t work.

Victoria’s right, of course. Some words are just funny. I mentioned the fact in a talk once (it’s one of my ‘go to’ lines), and when it came to questions at the end a woman offered the supplementary information that Pimlico is the only Tube station to share no letters with the word ‘badger’. This, needless to say, is now another ‘go to’ line.

An important point about ‘St John’s Wood/mackerel’ is its utter pointlessness. In a world full of Brexit projections and pronoun-angst, how wonderful is it to encounter a fact whose sole purpose is to make you laugh? Though not everyone gets the joke. Mention it in mixed company and half the people will roar with delight, while the other half will shake their heads in bewilderment.

My partner remains resolutely in the latter camp. These days her sigh of despair tends to appear before I’ve reached the apostrophe in ‘John’s’. Obviously this only adds to my fun. Similarly, the ‘Hull City’ fact is useful for winding up football bores, the sort who bang on tediously about flat back fours. Ask them: why are Hull City unique among the top 92 clubs? Leave them guessing for an hour or two, then reveal the answer: ‘Hull City’ is the only name that contains no letters you can colour in.

But it isn’t just about inanity. There is always, I would argue, something beautiful about uniqueness. The Tube network has 269 stations, but only one of them possesses the ‘mackerel’ quality. Just as Pimlico is unique in sharing no letters with ‘badger’. And Balham in sharing no letters with ‘Underground’. Or, indeed, with ‘Kevin Pietersen’.

Being nearly unique isn’t good enough. There are three countries that share no letters with ‘mackerel’ (Djibouti, Fiji and Togo). There are two winners of the Best Picture Oscar (Wings and Gigi). No one gets excited about those facts. But they do get excited about the only top-92 football club (Swindon Town), the only element of the periodic table (tin), the only US state (Ohio) and the only US state capital (Boston). They also relish the fact that Pierre, South Dakota is the only US state capital that shares no letters with its state.

Just one question remains: who first spotted ‘St John’s Wood/mackerel’? And how? It’s like the idea of putting wheels on suitcases — I appreciate its genius, but would never have come up with it myself. How was the fact born? I await next week’s letters page…