Jefferies Australia will come under intense scrutiny after US medicines giant Cosette successfully sought confidential modelling, which it says could prove Mayne Pharma provided incomplete financial information that ultimately led to its $672 million bid for the contraceptive pill maker.

The investment bank, led by veteran dealmaker Michael Stock, has been advising Mayne on the deal. Mayne is refusing to allow Cosette, which is backed by major private equity firms, to walk away from the transaction, a dispute that has sent the two parties to the Supreme Court of NSW.