With debt financing costs nearly doubling last year to €1.9 billion (£1.4 billion) it is now clear that Ferrovial, the Spanish infrastructure company, bit off more than it could chew when it bought BAA.

The £10.3 billion acquisition of the airports operator in 2006 was a triumph of debt over ability to pay - much like my mortgage.

The deal was financed almost entirely from debt but the Spanish company was confident that it could handle the liability because much of BAA's income is guaranteed years in advance.

Landing fees at Heathrow, Gatwick and Stansted are regulated and therefore easy to predict. BAA was a cash cow just asking to be milked. Unfortunately for Ferrovial the world has changed since summer 2006. Public outrage over the dilapidated state of Heathrow and frustration over long security queues has forced BAA to step up expenditure.

Meanwhile, the Civil Aviation Authority's review of airport charges for the next five years is expected to lead to lower revenue from the London airports than BAA had hoped.

When Ferrovial tried to refinance it was hit by the credit crunch.

Debt deals are struggling at the moment and Ferrovial's teetering mountain of debt could just be too risky to touch - hence the company's confirmation yesterday that it is drawing up plan B options.

Ferrovial needs to cut its liabilities and the only way to do so is to sell prize assets. It should raise about £1.5 billion in the next couple of months selling World Duty Free and some property but this may not be enough. The prospect of a key British airport, probably Gatwick, coming to market is getting a lot closer.

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