Why do last minute flights cost more?

Q Recently, I wanted to go to Madrid for the day, departing from any London airport on any day from Monday to Friday. Although I found relatively cheap flights with easyJet, British Airways and Iberia in the morning, the flights that left Madrid in the evening were expensive. Also, I noticed that flights gradually increase in price the nearer the departure date and time is. Is there any reason for this? I would have thought that if airlines can’t sell seats, they would reduce the price in order to attract customers. But this does not seem to be the case.

Name withheld

A First, let me tackle the question of whether fares should rise or fall as departure approaches.

The firm view of most airlines is that prices increase over time. The thinking is that close to departure travellers will be less price-sensitive – whether that is because they are business travellers whose companies are paying, or because they have urgent personal reasons for wanting to travel. This applied to me from Palma to Gatwick a few weeks ago, when I paid easyJet £240 for a two-hour flight a few hours before departure.

Occasionally you can find last-minute bargains; earlier in October I found a British Airways flight from Venice to Gatwick for just €38 (£34) the night before departure. But this is rare on any airline.

Regarding the fare differential between morning and evening flights: yes, Madrid fares do behave strangely. Looking at early January, it is easy to find cheap early morning outbound flights. I can see £20 on Ryanair from Stansted, £34 on Norwegian from Gatwick and £35 on easyJet from Luton.

Coming back, though, the only sub-£100 departure is easyJet’s late-evening departure to Gatwick, at £97. I can only speculate that there are relatively few departures in the evening, so airlines can keep fares high.

Personally in such circumstances I would fall back on the TAP Portugal option; the carrier always has good fares from Barcelona and Madrid via Lisbon to London, which allows you to visit the beautiful Portuguese capital as well as Spain’s capital. It’s my favourite way of getting back from these cities to Britain.

Every day our travel correspondent Simon Calder tackles a reader’s question. Just email yours to s@hols.tv or tweet @simoncalder