If no conclusions could be drawn about Gleeson's political leanings from delivering the Barwick address,Heydon says"there can be no rational basis to attribute to me any political affiliation with the Liberal Party".

It is an argument that might appeal to lawyers:counsel for the unions being backed into a logical corner by their own submissions.

But apprehended bias - which is about appearances rather than whether a decision-maker is in fact biased - is concerned with what non-lawyers would think.

Heydon says,nevertheless,the fair-minded observer could not have come to the conclusion he might harbour a political prejudice for a number of other reasons,including the nature of the Sir Garfield Barwick event.

It was,he says,an opportunity to deliver a"legal,non-political address".

While Heydon was sent emails pointing to the political affiliations of the organisers,and an invitation which solicited donations from people who could not attend,he says he did not read the latter and it is"notorious among the legal profession that I am incapable of sending or receiving emails".

The fair-minded observer could know nothing of this. But Heydon says,in any event,the fact donations were not solicited from attendees (who paid $80 for a dinner) supports the view the address itself was not a fundraiser.

His reasons are forensic and detailed but won't win over any detractors. The next round could be in the Federal Court.