Foreign companies are poised to snap up some of Britain's key airports if BAA is forced into a sell-off by regulators this week.

The Competition Commission is expected to call for BAA to give up one or two of its London airports and another in Scotland.

The regulator is concerned about the company's ownership of the three main London hubs, and its stranglehold on flights to and from Scotland.

A jet lands at BAA's Gatwick airport in West Sussex

The move follows a 16-month investigation into the Spanish-owned firm, which operates seven UK airports including Heathrow, Gatwick and Stansted.

Gatwick is seen as the most likely to go on the block with German construction group Hochtief and Australian bank Macquarie heading the queue.

It is also believed that Glasgow Airport and Stansted could be recommended for sale.

Since buying BAA for £10.3billion in June 2006, Spanish builder Ferrovial has been the focus of intense criticism for its running of Britain's airports.

The slow response to security alerts, monstrous queues, and poor service fuelled fears that Ferrovial was cutting corners to save cash as it struggled to pay off the mountain of debt it took on to finance the acquisition.

These concerns were underlined yesterday as BAA said it had completed a long-delayed £13billion debt restructuring.

This will give it £3billion for 'immediate' improvement projects across its portfolio.

BAA said £2.75billion had been earmarked for expansion to 'improve the passenger experience' at Gatwick, Heathrow and Stansted.

Another £255million will be spent on makeovers at Glasgow, Southampton, Aberdeen and Edinburgh airports.

The competition watchdog laid the ground for a break-up of BAA's monopoly with its preliminary findings in April.

BAA chairman Sir Nigel Rudd claimed the group has received 'huge expressions of interest' from potential buyers for Gatwick or Stansted. The potential sell-off has already sparked interest among overseas predators.

A host of private equity firms have also been touted as potential buyers, as well as Macquarie, one of Thames Water's owners.

Macquarie already has five airports, including Birmingham and Bristol, and is close to Ferrovial after advising the Spanish group on its acquisition of BAA.

The bank also bought Ferrovial's 20.9 per cent stake in Sydney airport, and its 50 per cent stake in Bristol.

London City airport owner Global Infrastructure Partners  -  a joint venture between investment bank Credit Suisse and industrial giant General Electric  -  has its eye on Gatwick or Stansted.

The only obvious UK-based buyer is Manchester Airports Group, which is owned by 11 local authorities around the city. It said it was interested in buying more airports and declined to rule out a bid for Gatwick.

However, MAG is unlikely to have enough cash to buy £1.8billion Gatwick on its own.

It is thought to be more interested in Glasgow, which could fetch £383million.