Airport operator BAA must sell Stansted Airport and either Glasgow or Edinburgh airports, the Competition Commission has confirmed.

BAA’s chief executive Colin Matthews said he was “dismayed” by the decision, claiming it would damage the company - which was investing in UK jobs.

Spanish-owned BAA runs six UK airports including Heathrow and has been the subject of a Competition Commission investigation since 2007.

In a March 2009 ruling, the commission said BAA must sell Gatwick as well as Stansted and either Edinburgh or Glasgow.

Gatwick was later that year sold to an investment fund called Global Infrastructure Partners, which owns London City Airport.

BAA said that sale, plus changes in Government policy that have ruled out new runways in south east England, have significantly changed the airport market.

It appealed the order to sell Stansted and a Scottish airport, but in a final report, the Competition Commission (CC) said the sale of the airports was fully justified.

The sale process will start in three months “or sooner if undertakings are accepted from BAA in the meantime”, the CC said.

Peter Freeman, the CC’s chairman of the BAA remedies implementation group, said: “Our report has been challenged, reviewed and upheld and it is clear that the original decision to require BAA to divest three airports (including Gatwick) remains the right one for customers.”

He went on: “The introduction of new ownership at Gatwick, while too recent for us to draw any firm conclusions, has given a foretaste of the benefits competition can bring.”

The CC said Stansted should be sold first as it served the larger number of passengers and there would be a small overlap between the Stansted sale and that of one of the Scottish airports.