"Do you have another travel document for this child?" she asked, lingering pleasurably on every syllable. She had our passports fanned out in her hand. "What?" "Er, no?" "Um, why?" we answered absent-mindedly. "Because this one expired two weeks ago," she finished triumphantly.

We stopped. Dropped jaws. Looked appalled. Stammered "oh no" and "what can we do?" The children got bored with watching adults talk and ran happily on to the plane. There was swimming and butterfly-chasing and castle-visiting on their minds.

"Get that person off the plane," snapped Ryanair lady, as the small blond head of the offending would-be traveller disappeared. "You must get that person off the plane now. That person is not allowed to board the plane."

So we ran after him to the plane, where he and his brother and best friend were already snuggled excitedly across the front row of seats, and consulted frantically - which parent would stay with which child, who would take which credit card, how to get an emergency passport, or just get off the plane and forget the holiday. Other passengers chipped in with suggestions and the happy holiday atmosphere turned to trauma as the five-year-old learned that he was being taken off the plane to go back to hot, sticky London.

As we came back down the ladder with Weeping Child, the picture of innocent woe, Ryanair Lady and her male counterpart, Ryanair Man, came to meet us. They were looking so steely that they were practically clanking. Ryanair Man had a clipboard and fluorescent clothing.

We whined hopelessly, "Is there no one at the airport who can extend the passport? Can we get EU-only passports within a day? Can we put him on mine? Or can't you turn a blind eye and tell us to get it sorted out when we get back? It's not the Soviet Union ... he is only a little boy, and we're only going to France."

Ryanair Man exploded. "It's not our fault his passport is out of date. If you want to go down this route Madam I can call the police and have you put in a cell for the rest of the day. He could be a terrorist."

My small son crumpled further. "Rules are rules," said Ryanair Man with splendid, gloating finality over the crescendo of sobs.

He was quite right. And, in a world where rules are rules, he was doing the right thing. Clearly we'd created the problem ourselves. With fears of terrorism leading to ever-tighter airport security, we should surely all be grateful for serious, thoughtful attempts to counter that threat - body searches, luggage checks, proper examination of documents.

Yet, equally clearly, Weeping Child was not a terrorist. (However hell-bent on destruction a five-year-old might be, even the most exasperated parent would agree he can do only so much damage). And it would have taken too much of a stretch of the imagination to think that he could be being trafficked to Carcassonne for some grim trade in adoption or truffled body parts by the two adults he called "mummy" and "daddy". What's more, neither Ryanair M nor W were really suggesting anything of this sort was amiss. They just appeared to be taking a slightly sadistic pleasure in enforcing the rules.

It didn't end too badly. After a day of hot bus rides and affidavit-swearing, Weeping Child and Angry Daddy were on the same plane out of Stansted at dawn the next morning, £300 poorer after buying more tickets and paying the emergency rate for a new passport, but otherwise unscathed.

Ryanair Woman, still looking steely, was on duty again. As she gave Weeping Child's new passport a long, wordless stare, it was Angry Daddy's turn to get waspish. "Ryanair should nominate you Employee of the Month for the extra revenue you've generated," he said. "People should just stop moaning," she answered.

Well, no. We shouldn't stop moaning. We're the customers, even if we're not always right. We all love Ryanair. Those cheap cheap flights might help to pollute the atmosphere, and it might feel a bit alarming to fly on a plane so sparsely furnished that even the sick bags seem to have been phased out, but they do let us take lots of lovely holidays for almost nothing. Things would have to get a lot worse on the customer-relations front to actually stop us using them.

The best-case scenario (for us) would have been for the airline to have agreed with the Home Office to have an immigration officer staff Stansted and other major tourist airports during the holiday season, giving quick-fix help to innocent travellers who've got themselves into bureaucratic pickles. That sounds so fabulously sensible and simple that there's sure to be a reason why it's impossible.

But failing that, couldn't they take just a bit more trouble to please? It needn't cost extra.

Slices of London: e-mail Urban Fox here