BAA, the airports operator, will complete a near £13 billion refinancing this week as it prepares for the biggest shake-up to its business for more than 40 years.

The Competition Commission is expected to confirm on Wednesday that it considers BAA’s ownership of London’s three largest airports to be against the public interest and to call for the disposal of at least one, Gatwick.

BAA has conceded that a break-up of some sort is inevitable and it is understood to have structured the bond issue at the heart of its refinancing in a way that is not dependent on it retaining all seven of its UK airports.

A pricing review and the onset of the credit crunch have delayed the refinancing for the two years since Ferrovial, of Spain, bought BAA for £10.3 billion.

A source close to the company said that the completion was a milestone that would make it far easier for BAA to raise capital in the coming months as it prepares to enter a new era.

BAA has owned seven of the country’s largest airports, including Heathrow and Gatwick, since 1965. The Competition Commission in April outlined a case for a break-up of the business by arguing that there was no competition between BAA’s London sites and very limited competition between its main Scottish airports in Glasgow and Edinburgh.

International infrastructure groups have approached BAA with offers to buy Gatwick for £3 billion before Wednesday’s provisional findings from the commission. Manchester Airport Group last night emerged as a a bidder for Gatwick. Other bidders are understood to include Hochtief, of Germany, Macquarie, of Australia, and Dubai International Capital.

Sir Nigel Rudd, the BAA chairman, said this weekend that there had been “huge expressions of interest” for Gatwick and Stansted, but insisted that neither was for sale at present.

It is thought that BAA is ready to sacrifice Gatwick if it means keeping Stansted within its portfolio.

Analysts believe that a sale of Gatwick and Edinburgh could represent a significant opportunity to raise funds for the business, despite the slowdown in the airport sector since the beginning of the summer.

Sir Nigel conceded that a break-up would not be a “disaster”, but said that it could prove harder to fulfil the airport expansion desired by the Government if Britain’s most important sites were under different ownership.

BAA has long argued that better regulation would prove more effective in improving standards at the airports than a break-up of its portfolio.

The Competition Commission’s report could prove potentially embarrassing for the Government by questioning its decision not to consider Gatwick as the site for a new runway in the South East. Gatwick was ruled out in 2003.

BAA refused to elaborate on Sir Nigel’s comments yesterday. A spokesman said: “We are going to have to wait and see what the Competition Commission’s findings are.”

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