BA & IB are combining their operations between LHR - MAD/BCN and will share all revenue and profits on both routes. The venture will come into effect Jan 01.
The two airlines have received antitrust immunity from the EU which allows them to "collude" legally.
Together they hold about 50% of the market from London to MAD/BCN with competition coming from BMI, Easyjet and Ryanair.
Maybe a "full merger" could be in the works.