Glasgow and Aberdeen airports are being put up for sale, owner BAA has announced in a statement issued through Heathrow Airport Holdings (HAH).

Spanish-owned BAA says it "is now formally entering a sale process". Although the potential buyer is unknown, it is thought that it could be HAH's biggest shareholder - the Spanish transport infrastructure ­giant Ferrovial.

"Whilst there is currently no certainty that a sale will be concluded, the group intends to work towards completing a transaction by the end of the year," a HAH spokeswoman announced.

Ferrovial - which holds a 25 per cent stake in the airport operator  - is rumoured to have tabled an £800 million bid for the airports, along with Southampton Airport.

Formerly the British Airports Authority, BAA once ran Gatwick, Stansted and Edinburgh airports, in addition to its current holdings. However, concerns about the group's monopoly position led to the Competition Commission ordering the sale of those assets.