BAA has negotiated a £625 million four-year deal to refinance some of its debts.
The airport operator said the deal marks "significant progress" towards refinancing the group's £1.57 billion worth of subordinate debt.
It has borrowed the money from eight major international banks.
BAA had originally planned to take a loan of £500 million, but decided to increase the size "to meet significant excess demand from new and existing relationship banks".
The remainder of the £1.57 billion will be paid off with further loans, or by selling off "non-core" assets, said BAA.
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