If you compare the route maps found at the back of the British Airways and Iberia in-flight magazines, some large holes appear.

From its base at Heathrow, BA is strong going west to the US and east to Asia, especially the old colonial cities of Singapore and Hong Kong.

Iberia’s traffic, meanwhile, is strong going south into Africa and southwest towards Spain’s old empire in Latin America.

Put the two networks together and there are few overlaps, which offers the two airlines an opportunity to get British passengers on to Iberia flights to South America and Spanish passengers on BA flights to the US and Asia.

In the short term, this should make life easier for passengers because booking flights, arranging itineraries and collecting air miles will be simplified.

In the long term, however, passengers may notice some significant changes to the way BA and Iberia organise their flights. Heathrow, one of the world’s busiest international airports, is effectively full, and, with the Conservatives against a third runway, the scope for growth is limited.

That means that BA’s growth is also constrained, so to increase revenues it needs another base. Madrid, with its new Richard Rogers-designed airport terminals, could provide that space.

For example, BA may decide that it does not need to operate a direct flight from London to São Paulo in Brazil, as it could send passengers through Iberia’s hub in Madrid instead. This would free up a slot at congested Heathrow for another flight, perhaps to New York.

Alternatively, the combined BA-Iberia could decide that there is sufficient demand to start direct flights to Seoul in South Korea but a lack of space at Heathrow might mean that the flight would have to leave from Madrid.

These changes could mean that British passengers will have to get used to changing planes in Madrid for flights to all but the world’s major cities.

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