The relationship between Birmingham Airport and its very small rival 15 miles down the A45, Coventry Airport, has never been an easy one.

Occasionally the two businesses have rubbed along and claimed to be complementary to each other, but more often a state of bitter rivalry exists.

It would appear that the uneasy neighbours are about to enter another difficult stage.

Birmingham Airport chief executive Paul Kehoe, not a man to mince his words, is clearly rattled at the probability that low-cost holiday flights will soon resume from Coventry Airport, which is now owned by Birmingham businessman Sir Peter Rigby.

You don’t need a degree in economics to understand Mr Kehoe’s concerns. Birmingham Airport’s finances are stable, profits even rose by £5 million last year although that was achieved largely by axing jobs. But in difficult times for the aviation industry, even a minor competitor can be a major threat.

Two years ago, Mr Kehoe described the business case for Birmingham Airport’s runway extension plan as marginal at best. The cost of this work has been cut, and the runway is to be built, but it is difficult to imagine in the current economic climate that the business case is much more robust.

Birmingham Airport’s problem is that in a free market system, the likes of Sir Peter Rigby can quite easily offer niche aviation services, make some money and take customers away from established operators.

This, like it or loathe it, is called capitalism and is what creates wealth and jobs in this country.

There’s no disputing the possible threat that Coventry Airport poses to Birmingham. Mr Kehoe talks about losing 500,000 passengers, which would take a significant part of Birmingham Airport’s profits. He doesn’t state that the runway extension might be in danger, but that is the clear implication.