Reuters was first to report that Spanish infrastructure firm Ferrovial is looking at options for its 25% stake in London’s Heathrow and has held preliminary talks with advisers on the future of its holding in Britain’s biggest airport. Ferrovial’s Heathrow stake has drawn interest from private equity firm Ardian, which has studied a joint offer with Saudi Arabia’s Public Investment Fund. Heathrow airport is valued at about 26 billion euros including debt. Shares in Madrid-listed Ferrovial rose as much as 4.2% after Reuters revealed the news. At market close they were up 3.7%, scoring their second-best day in five months.