BAA, the owner of Heathrow and Gatwick, may have to bring forward the sale of one of its airports amid concerns that it will be unable to complete the £10 billion refinancing of its debts.

The airports operator said yesterday that its investors had agreed to stump up an extra £400 million in funding to help to improve the chances of a refinancing being achieved. The extra cash is needed to enhance the company's credit ratings, which were cut last month to one notch above junk.

The refinancing difficulties mean that the sale of Gatwick, which could raise at least £2 billion, could be accelerated. Macquarie, the Australian investment bank, has been advising BAA for several months on the possible sale of assets. Shares in Ferrovial, the Spanish majority owner of the British airports group, fell sharply in Madrid over concerns that the refinancing might not be achieved.

The problems precede a significant increase in BAA's interest charges, which are scheduled to rise next month, according to people familiar with the company. Last year the gross interest payments for BAA and its financing vehicle, ADIL, were £964 million - more than the £956 million that BAA generated in earnings from all its airports.

Ferrovial holds 62 per cent of BAA, and the remainder is shared between Caisse de Dépôt et Placement de Québec and GIC, the Singapore sovereign wealth fund.

BAA said that it had not finalised aspects of its refinancing plans, noting that it had not completed the rating process or received sufficient commitments from its lending banks to transfer a tranche of debt into a new, ring-fenced funding structure, backed by its London airports and the Heathrow Express. So far only the European Investment Bank has announced that it has signed up to the bond transfer.

While negotiations with its banks continue, the group intends to begin consultation with bondholders, who hold about £4.7 billion of BAA debt that was in the market at the time of the 2006 take-private deal, through the Association of British Insurers (ABI).

However, the airports group gave warning that credit market difficulties could affect these plans. “BAA may not ultimately be in such a position [to begin negotiations] owing to continuing challenging market conditions,” the company said.

A BAA spokesman insisted that the company had sufficient cashflow to service its debt and intended to stick to its timetable of completing the refinancing by the end of the third quarter.

The ABI, which represents most of Britain's big pension funds and institutional investors, has been asked by BAA to conduct a bondholder inquiry to try to establish the identity of BAA's bondholders.

The refinancing problems emerged on the day that BAA confirmed that it would move long-haul British Airways flights to New York - and seven other destinations - into Terminal 5 next month.

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