Around 6am tomorrow – barring a couple of improbable scenarios – I will join (and thereby increase) the queue for security at Heathrow. Then I shall walk through to the departure gate to board a flight I do not wish to be on. My presence on the two-hour trip will cost the airline a lot of cash, and incrementally damage the environment. But the reason I shall drag myself reluctantly on board is to save £120 – the penalty that the airline will impose were I to choose not to fly.

Let me explain the circumstances, then see if you can discern any sense in the airline's behaviour.

I booked British Airways flight 478 from Heathrow to Barcelona a month ago. BA was a willing seller, and I was a willing buyer, at a fare of £101 return; since then, the price has more than doubled to £237. I understood that locking in to a good-value ticket brought the risk that my travel plans might change, and that I would lose the cost of the flight.

In part, that is what happened. My plans now call for me to fly instead to Zaragoza, a route that only Ryanair serves, though I still intend to fly home from Barcelona using the return half of the BA ticket that I bought.

It seemed only reasonable to call British Airways to cancel the outbound leg. I was not seeking any kind of refund, merely informing the airline that it could re-sell the outbound seat – making some money, and allowing someone else to travel to the beautiful Catalan capital. I wasn't expecting thanks – but neither was I expecting to be told flatly, "If you don't fly out, you can't fly back."

Having tracked the often-ludicrous pricing strategies of airlines, I am well aware of the propensity for some one-way fares to cost more than a return. The airlines justify this topsy-turvy view of the world because business travellers – who are held to be less price-sensitive – comprise the main market for one-way flights. Check out BA's flights to New York; fly out next Saturday from Heathrow to JFK and you will pay £524 one-way in economy, but pretend to want to fly back on the Sunday, and the fare falls by £200 – yes, 40 per cent off for a journey twice as far. If you fail to show up for the flight home, the airline is powerless. So the rational traveller buys a return but throws away the inward leg.

In the bad old days before no-frills airlines, a similarly strange universe prevailed in Europe. Pre-easyJet, the cheapest return flight to Barcelona cost about the same as I paid – around £100. But anyone who needed to leave the Catalan capital without staying over a Saturday night would pay £500 return. Unsurprisingly, crafty travellers came up with all sorts of wheezes to try to reduce these punitive prices. And in return, the airlines imposed a raft of rules to prevent what is technically known as "tariff abuse".

In came Stelios Haji-Ioannou, the founder of easyJet. He said he couldn't care twopence whether you flew one way or return, nor how long you stayed at your destination. The traditional airlines were appalled, but when they saw how much custom they were losing to the no-frills carriers, they abolished the "Saturday-night stay" rule for European flights.

Two years ago, British Airways went one stage further, and started selling so-called "sector" fares – the revolutionary idea being that you could buy one-way tickets to or from Barcelona, and if you chose to book a return flight it would simply cost the sum of the one-way tickets. Some sanity, at last – or so I thought. But the archaic rule still prevails: when a passenger doesn't show up for an outbound flight, their inbound trip is automatically cancelled.

If the traveller is a genuine "no-show", this rule has a certain merit:if they haven't gone, they won't be coming back. But when a passenger goes to the trouble of informing the airline they won't be going out, it seems bizarre to say they will need to pay again to fly home. From almost all the points of view that I can identify, such corporate intransigence is a cost, not a benefit, for the airline.

The only possible benefit to BA is something of a throwback to the bad old days. Perhaps the logic goes like this: the only airlines that fly between Barcelona and Heathrow are British Airways and its partner, Iberia. Therefore, if I don't make the outbound flight, I can be forced to buy a ticket for the same inbound flight all over again, which will cost me an extra £120 – in effect, the penalty that BA seeks to extract by making me book again.

Since I am reluctant to do that, I will turn up at Heathrow feeling even more grudging and grumpy than usual, and be less inclined to consider the airline when planning future European trips. From Barcelona I shall travel overland to Zaragoza, resenting the fact that the train fare costs more than a Ryanair flight from Stansted to the Aragonese city.

So much for my costs; British Airways must hand the Chancellor £10 air passenger duty, and BAA Heathrow a fee of about the same; both costs apply only to people who board the plane, not those who are merely booked on it. Had the airline accepted my cancellation, it would escape these fees. And BA could probably resell the seat: a glance at shows the average one-way fare for its flights from Heathrow to Barcelona tomorrow is now £500, which shows how heavy demand is. I would love to know the airline's rationale for happily turning away a prospective passenger, prepared to spend a small fortune on the flight. Instead, BA will carry a curmudgeon to Catalonia who intends to make the most of the complimentary cocktails: another Bloody Mary, please.

... and how to avoid getting on board?

Heathrow at dawn is the unappealing prospect that awaits me tomorrow; but should one of those "improbable scenarios" come to fruition, it may yet mean I need not actually get on the Airbus to Barcelona. My challenge: to convince British Airways that I have flown outbound, and thereby dissuade the airline from cancelling my inbound reservation. (Ryanair, which carries more passengers, more profitably, does not apply its rules with the same rigour: if you don't show up for your outward flight, you are still welcome to take your seat for the inward leg.)

One dodge that I have already discounted, on the grounds that it is completely illegal, is that I persuade either the excellent Nicholas Crane or the illustrious Louis Theroux – both of whom I am frequently accused of being – to borrow one of my passports and fly to Spain.

Of the "legal" options, the least likely is that you share my name, have a valid passport and would like to fly from Heathrow to Barcelona tomorrow. If you have, turn up good and early at Terminal One, quote the booking reference 22D4SZ and off you go. When I arrive and find you have already checked in, I shall happily wander off to Stansted and the flight to Zaragoza for which I have already procured the boarding pass (below, left). Just promise you won't turn up at Barcelona for the return leg.

The other possible scenario: that you work for British Airways, and know for a fact that if I check in but do not actually board the aircraft, then I will still be allowed on the homebound plane. People I have spoken to at BA flatly deny that this is possible, but you may know better. Convince me (via that my inbound flight is safe, and I shall check in for BA478 but fail to show up at the gate.

In future, I shall circumvent BA's absurd rule by spending a little extra time booking two one-way flights instead of a simple return trip. You might want to do the same.

Travel is tricky, but not travelling can sometimes be even tougher.