Ferrovial, the controlling stakeholder of BAA, has put 10 percent of the airport operator up for sale in a bid to cut its debt burden.

However the Spanish infrastructure group is looking to sell to a single buyer, in a move that would see it remain the operator’s largest shareholder, however its controlling stake would fall from 56 percent to 46 percent.

As well as raising cash, the sale would enable Ferrovial to de-consolidate BAA from its accounts because it drops below 50 percent. This would relieve it of €15bn of debts relating to its six UK airports, including Heathrow and Stansted.

The Madrid-based group has been under extreme financial pressure since buying BAA – it has debts of £22billion, of which £13billion is made up by BAA.

It is understood Ferrovial would be willing to sell more of BAA if it successfully offloads the 10 per cent chunk.

The other main shareholders of BAA Canada’s Caisse de depot et placement de Quebec, which controls 26.48pc, and Singapore’s GIC, with 17.65pc.

Regulators forced BAA to sell Gatwick and potentially two other airports. Meanwhile the financial crisis has dented passenger numbers and the bottom line.

Íñigo Meirás, Ferrovial’s chief executive, said “any sale will depend on the offers received. The process we have initiated is in line with our strategy to establish a market valuation of our assets.”

Ferrovial denied the move could be the first step towards an exit from BAA or a demerger, Mr Meirás said: “We would like to underline that our commitment as a long term investor in BAA remains in place.”