My flight was late because ...

British Airways flight 453 from Ibiza to Heathrow departed 18 minutes late last Sunday. Nothing unusual there – until you learn the cause. It wasn't foggy, it was Misty.

Misty Gale, her husband Matt and toddler Soren had booked well in advance for the flight. The family of three from London were obliged to make two separate bookings because of a strange glitch in the airline's system. Buyers cannot combine passengers who want the cheapest cabin-baggage-only fares on the same reservation as travellers who check in cases.

"We only wanted one hold bag between us. So I booked my flight, with a bag, separately, and another cabin-baggage-only booking for Matt and Soren," Misty tells me.

The family arrived at Ibiza airport in good time for their flight home. Matt and Soren were able to proceed as normal – but Misty was told there were no seats left.

Many airlines sell more seats than there are available for flights that are strongly in demand. They use past experience to predict how many passengers will fail to show up for a particular departure. Often, they guess right: passengers reach the airport late, or arrive on delayed connecting flights that don't connect, or change their plans and don't bother to cancel a non-refundable ticket.

Overbooking, when properly implemented, is an excellent device for airlines and passengers alike. It allows people who need urgently to travel to buy tickets even when no seats are available. and means planes fly fuller – better for passengers in the form of lower fares, and better for the planet. But sometimes after a big event such as last weekend's Ibiza Music Video Festival, the airline's prediction turns out wrong. When everyone shows up, usual practice is to offer inducements to passengers who have the flexibility to travel later. In the United States, where overbooking is an art form, a departure-gate auction takes place. The airline gradually raises its offer until sufficient passengers bite. They offload and collect their cash, while everyone desperate to fly takes off.

Boarding-gate bribery never took place on that sunny afternoon in Ibiza. Instead, ground staff told Misty she and three other passengers were going nowhere: "Ground staff didn't ask if any other passengers would be willing to fly later for a wedge. They just told us we couldn't get on the flight as there were no empty seats."

Making a seat pitch

"No empty seats" wasn't quite accurate. For the past few years, BA has sought to raise the perceived value of its Club Europe product by guaranteeing that the middle seat of three will remain empty. So a "full" flight with five rows of Club seating actually has 10 empty places.

Matt, Misty's husband, had spotted this on the way through to economy, and hatched a plan. He made what can only be described as a seat pitch. Misty takes up the story: "Matt, who doesn't like attention, put himself in the spotlight – a crying toddler at his ankles – by asking the passengers in Club if anyone would allow me to take up one of the empty spaces."

Meanwhile, the captain became aware that Misty needed to travel with her family, and arranged for her to fly in the jump seat to keep the family united. He instructed the door to be opened and for the payload to be increased by one with the addition of Misty. (He also saved BA €250, the mandatory compensation for overbooking on short European flights.)

Evidently you get an excellent grade of passenger in Club Europe, because Misty was invited to travel in comfort. Celebrity lookalike photographer Alison Jackson and actress Annette Mason (the wife of Pink Floyd drummer Nick Mason) said they would be delighted for Misty to interpose herself in their row.

Once everyone was on board, the flight airborne, and the inflight sales began, Matt sent Alison and Annette each a box of Charbonnel et Walker chocolates as a thank-you. "This broke the ice and resulted in them swapping stories and contacts, as they had many friends in common," says Misty. Though she was relieved to be on board (and indeed upgraded, after a fashion) she adds: "I am shocked that BA would behave like that. I am a pretty seasoned traveller so am embarrassed to be caught out like this."

Ironically, a good way never to be offloaded for space reasons is to fly only on Ryanair, which tells me it never overbooks. Furthermore, because Ryanair has only one model of plane – the Boeing 737-800 – there is never the risk that a late plane substitution could jeopardise journeys.

On another airline, I was grounded in Madeira when an A321 was replaced with a smaller A320 – but because I had accepted a €400 bribe to re-route via Lisbon, I was perfectly happy.

Jumbo shuttle

Another delayed BA flight on Sunday (by 42 minutes, if you're counting) was the final departure from Glasgow to Heathrow. Unlike my Madeira flight, it was upsized, not downsized. BA1497 is normally a one-class Boeing 767. But the Sunday shuttle was instead operated by a 747 Jumbo jet.

A spokesman for BA said: "It is extremely rare for us to use a Boeing 747 on a domestic route ... and was due to the fact that the 767 due to operate the service had a technical problem."

Some lucky passengers enjoyed flat beds in First and Club World, while others stretched their legs in World Traveller Plus. The airline tells me the upgradees were selected randomly. With only 250 passengers on board, even cattle class had plenty of room to move – according to my calculation, everyone could have had an empty seat next to them, in the style of Club Europe.