But there's one group, ever present at any major airport, that's never likely to be filmed. At Gatwick, you find them by going round the back of Thornton's chocolate shop, then along a corridor that looks as though you're not allowed to go down it: the sort of corridor in which you expect to overhear whispering criminals plotting to kidnap an ambassador. Then up a lift and past a bloke who apologises for charging you pounds 1.50, and there they are: the plane-spotters.
There may seem to be a peculiarity at the heart of this hobby. Bird-spotting, for example, offers a challenge. If a species can be found only on the Faroe Islands, and you have to take a boat there and then crawl through the woods at 5am to catch a glimpse of this rare bird through the undergrowth, that represents quite an achievement. It doesn't carry quite the same glory to succeed in spotting a plane at an airport.
But next time you're on a plane that's landing, remember as you're thinking "Phew, still alive then", or "I'm about to see my son for the first time in 20 years", that a line of blokes are ticking you off as the second DC166 since Thursday. "All day yesterday I was waiting for an AH," said Simon. "Then five minutes after I left, it arrived." Isn't that always the way?
But this is the point.As with their more famous trainspotting cousins, the first aim of plane-spotters is to collect numbers. They divide into two groups: those who collect all numbers, and those who collect one particular plane. Which is why you'd be hacked off if you were a collector of AH numbers and the bastard didn't turn up. So specialised is this group that if a spaceship hovered down, they'd throw their arms up in exasperation about poxy aliens blocking the runway, and complain that now there was nowhere for the AH to land, they might as well go home.
So they wait for their plane, and then they write down the number. All day. "I normally come here first, and then go to Heathrow," said Derek, who's been coming since 1978.
The coffee-shop staff know them all personally, although the spotters don't drink much coffee. Instead, they bring zip-up bags carrying binoculars, notepads covered in numbers, Tupperware boxes of sandwiches, and bottles of diluted orange squash they've prepared earlier. Which makes them look quite cute, like 40-year-old cub scouts on an outing.
As this dedicated line of around 30 spotters rubs its hands to keep warm, the uninitiated can't help but wonder why. I began to wonder whether they'd think I was weird if I told them that I preferred to go dustcart-spotting. And that there was a B6578 that I'd seen every Monday for eight years, even after it was moved from Lambeth to Croydon because it didn't suit the wheelie-bins. Would they think I was at all odd if I said I had a mate who went to fairgrounds all over the country to go dodgem-spotting?
Yet you can't help feeling, as each plane roars off the runway to a flurry of felt pens on exercise books, that there is a rationale to this pastime. For deep down, the spotters do sense that with every take-off and landing, they're recording a momentous event.
By comparison, last year I was on a plane about to take off from Barbados and destined to land at Gatwick, where no doubt it would be spotted. As the captain was doing his opening routine, he announced that owing to the wind flapping the wrong way, we'd be landing 25 minutes later than scheduled. "Oh!", belched the woman in the next seat to mine, throwing her arms in the air, "Isn't that typical."
Clearly, the fact that she was about to cross continents gave her no sense of occasion. Instead she was probably thinking, "I was hoping to nip back from Bridgetown and get home in time for Heartbeat."
Whereas plane-spotter John was as captivated as ever by the importance of the events he was witnessing. "The marvellous thing about an airport," he said, "is looking at everyone in the departure lounge, and wondering what they'll all be doing tomorrow. You look at a queue of people, and maybe the first one's a dodgy geezer who'll be in Thailand buying drugs; she'll be at a funeral in Turkey; and he'll be having a bunk-up in Norway."
Every plane that passed overhead, he said, fascinated him because it contained a hundred stories. Why this led him to write down the number of the thing in a book, he wasn't sure. It's a pointless pastime, but then so is everybody's, unless your hobby is something like road-sweeping or mending the ozone layer.
In pursuing this pointlessness, John had been arrested twice. "The first time was in northern Greece, when we broke into an airfield. That was a laugh." Though, for all we know, they were suspected of being Turkish spies. The numbers they'd written were handed to a crack team of codebreakers, and the orange squash was delicately buried underground and blown up in a controlled explosion. "Then I got arrested for breaking into RAF Mildenhall with my mate. He was obsessed with this plane that could only be spotted at this American air base. So we slipped under the fence, but they caught us. But he spotted the plane, so we could tick it off.".
They were kept overnight, he said, but once the Americans accepted that they were plane-spotters, they gave them a big breakfast and showed them round the whole airfield.
So could you really write this hobby off as boring? How many DIY enthusiasts would take on the most powerful military machine in history, for a glimpse of their favourite Rawlplug? How many gardeners would risk solitary confinement for a chrysanthemum?
Every hobby is pointless. The trick is to recognise your own as such, and then pursue it with ludicrous dedication.
So, a banker of a TV series would be a drama about a plane-spotter and his assistant, breaking into top-security establishments and uncovering conspiracies to hide the truth about the whereabouts of their favourite plane. It could be called "The AH Files" and subtitled "The bloody thing must be out there".
Maybe Saddam's a plane-spotter specialising in Stealth bombers. And the only way he could tick it off was to kick out the weapons inspectors. So on the first night of the bombing, he was on the roof of his palace screaming "Got it at last."