LONDON -- BAA, the world's biggest airports operator, is preparing to repel unwanted takeover approaches as investors bet its rejection of an unsolicited 8.75 billion pound ($15.3 billion) offer from Spain's Grupo Ferrovial will flush out rival suitors for the UK-based firm.

Ferrovial, a construction, infrastructure and services group, will lobby leading institutional shareholders in BAA this week before deciding whether to mount a hostile bid for the company, which operates London Heathrow, the world's busiest international airport and Europe's third-largest air cargo hub after Frankfurt and Paris Charles de Gaulle.

Ferrovial has said it is willing to improve its offer if BAA allows it to conduct a restricted due diligence and recommend an agreed takeover to shareholders. BAA, which owns seven UK airports, including London Gatwick and London Stansted, a leading cargo and express hub, rejected the offer.

BAA said Ferrovial's offer did "not begin to reflect the true value of BAA's unique portfolio of airport assets."

Meanwhile, Macquarie, the Australian bank which has stakes in several airports, is reported to be mulling an offer for BAA and has been talking with U.S. private equity groups and Canada's Ontario Teachers' Pension Plan about a possible bid.

Bruce Barnard