BAA, the UK airport operator, has raised the stakes in its battle to stave off an £8.8bn (€12.9bn) hostile takeover bid from Spanish conglomerate Ferrovial by telling shareholders its real worth is more than £10.2bn.

The valuation, revealed in a defence circular sent to BAA shareholders today, is 16% higher than Ferrovial's offer and 13% above BAA's market capitalisation based on yesterday's closing price of 834p.