But Mr O'Brien's rationale for secrecy is under challenge on two fronts. Lend Lease has confirmed it may bid for the second stage itself, in which case it would have exclusive knowledge of the government payments - a situation clearly at odds with competition.

The case for secrecy has been challenged by Melbourne University infrastructure expert Colin Duffield, one of the few Australian academics to have made a detailed study of the economics of public private partnerships (PPPs).

"East West stage 1 is a done deal," said Associate Professor Duffield, who called for the project to be scrapped last week. "The winning Lend Lease-led consortium know the figures. I am confident the losing bidders would have a fair understanding of the figures. Why shouldn't the public know? It is the public paying for it after all."

Associate Professor Duffield said the government payments to the Lend Lease consortium on the first stage of the project would have little relevance for the second stage, which is now in the planning phase.

"In keeping with Treasury policy on such projects, stage 2 will have its own budget and no doubt will be structured to maximise efficiencies for the community. The logic for not releasing the availability payment figures on stage 1 is not self-evident. It is a mystery to me."