A sale of Australia's biggest airport moved closer on Monday as an infrastructure investor group won permission to conduct due diligence on Sydney Airport Holdings Pt Ltd, after sweetening its takeover offer to A$23.6 billion ($17.4 billion), Reuters reported. The move sent the airport's shares up 5%, with analysts saying a rival bid appeared unlikely given the scale of the funding needed and foreign ownership rules that mean the airport must remain 51% Australian owned. Sydney Airport is Australia's only listed airport operator and a purchase would be a long-term bet on the travel sector which has been battered by the pandemic. The country plans to gradually open its borders once 80% of adults are fully vaccinated, a milestone expected by the end of the year. A successful takeover would be among the largest buyouts ever of an Australian firm and underline a year of stellar deal activity, that has already seen a mega $29 billion buyout of Afterpay by Square. The improved offer of A$8.75 a share - an increase of 3.6% - follows prior proposals from the consortium pitched at A$8.45 and A$8.25, both of which were rejected by the airport operator's board as inadequate. Read more.