Grupo Ferrovial has endured a bruising round of meetings with some of BAA's biggest investors after the airports group rejected its £8.7bn takeover approach.
Advisers to the Spanish infrastructure giant spent last week visiting BAA's shareholders to discuss the indicative 810p-a-share offer. They will continue to present to investors this week before meeting with Ferrovial's management, which will then decide whether to increase its offer for the owner of Heathrow and Gatwick or to walk away.
"They are definitely serious and I don't think for one minute they will walk away from this," said one major shareholder. But the investor added that the 810p offer had been seen as derisory. He said of the presentation: "We fell about laughing at their offer and eventually even they were laughing, too."
It first emerged earlier this year that Ferrovial was interested in BAA, with an indicative offer finally being put to the board at the start of March. BAA instantly rejected the approach, however, and said it did not believe it was in shareholders' interest to enter discussions.
Since then, the Takeover Panel has told Ferrovial it has until 24 April to make a firm bid - known as "put up or shut up" deadline.
Analysts had predicted a higher offer, with some believing Ferrovial will need to bid well above 900p to secure BAA. Combined with its debts of around £5bn, that could end up costing a total of around £15bn.
It is thought, however, that the company put in a low initial approach as it is concerned that rival groups are also considering a tilt at BAA. Australian investment bank Macquarie is seen as the most likely rival.
"No one else will have been working on this for a year [as Ferrovial has]," said one City source, "but there will be people out there who are burning the midnight oil."
Ferrovial has spent most of this year putting together a consortium, which includes Canadian investment fund Caisse de dèpôt et placement du Québec and Singaporean fund GIC. Debt finance is due to come from Citigroup, Royal Bank of Scotland and Banco Santander Central Hispano.
Macquarie was originally tipped as a potential member, as it jointly owns Bristol airport with Ferrovial.
BAA, which was privatised 19 years ago, is committed to an extensive investment programme, including spending £3bn on Stansted and £4bn building a fifth terminal at Heathrow. Ferrovial is understood to have assured investors that it plans to continue with the investment programme.
As well as Bristol airport, Ferrovial's other UK interests include a share in the Tube Lines consortium through Amey, the support services specialist it acquired three years ago. Tube Lines is responsible for the upkeep of the Northern Line.