BAA's ownership of London's main airports was under threat today after the operator was referred for a full-blown competition inquiry.
Britain's Office of Fair Trading said it had decided the supply of airport services by BAA merited further investigation by the Competition Commission.
BAA runs seven UK airports, operating at Stansted, Southampton, Glasgow, Edinburgh and Aberdeen, as well as at Heathrow and Gatwick.
The move by the OFT comes after it said in December that it was minded to refer the company to the Commission. A subsequent consultation process drew more than 60 responses from parties including airlines and consumers.
In December, the OFT said it believed the current market structure did not 'deliver best value for air travellers in the UK' and added that greater competition could bring significant benefits for passengers.
In the South East of the country, the OFT said it found that BAA's airports handle nearly 90% of passenger trips, adding that these airports could, under separate ownership, compete to attract air passengers.
BAA's major airline customers have long pushed for a full investigation, with relations further strained in the summer by arguments over the implementation of enhanced security measures at London's main airports.
The operator's investment plans have also been criticised, with Ryanair boss Michael O'Leary recently angry at BAA's plans for a '£4 billion gold-plated Taj Mahal' at Stansted, which he believed could be built for £1 billion. BAA is owned by Spanish construction firm Ferrovial after a takeover last year.
Ryanair today welcomed the investigation.
