Former attorney-general George Brandis has warned of the challenge that right-wing populism poses to the Liberal Party, in his valedictory speech to the Senate ahead of taking up the post of high commissioner in London.

Brandis, a Liberal moderate, also strongly cautioned the Coalition against listening to those who said it should use national security as a political weapon against Labor, and criticised attacks on the judiciary from his own side.

With Prime Minister Malcolm Turnbull looking on, Brandis told the Senate that classical liberal values were under “greater challenge than at any time in my memory”.

“Increasingly, in recent years, powerful elements of right-wing politics have abandoned both liberalism’s concern for the rights of the individual and conservatism’s respect for institutions, in favour of a belligerent, intolerant populism which shows no respect for either the rights of individual citizens or the traditional institutions which protect them.”

Brandis was attorney-general throughout the Abbott and Turnbull governments, leaving the ministry in the December reshuffle.

He became increasingly outspoken as a voice of the moderate strand of the Liberal Party toward the end of his time in parliament. Within the government, he was critical of the home affairs minister, Peter Dutton, a hardline conservative.

In his speech Brandis targeted “right-wing postmodernism”. “A set of attitudes which had its origin in the authoritarian mind of the left has been translated right across the political spectrum,” he said.

“This presents a threat both to liberalism and conservatism, and a profound challenge to the Liberal Party as the custodian of these philosophic traditions.”

Brandis – who once set off a political storm by declaring that people had the right to be bigots – said being a liberal wasn’t easy.

“It means respecting the right of people to make choices which we ourselves would not make and of which may disapprove.

"It means respecting the right of people to express their opinions, even though others may find those opinions offensive.

"It means respecting the right of people to practice their religion, even though others may find the tenets of that religion irrational.

"It means, in a nation of many cultures, respecting the right of people to live according to their culture, even though, to others, that culture may seem alien.

"It means respecting the right of everyone to marry the person they love, even though others may find their understanding of marriage confronting.”

Brandis was a prominent figure pushing for same-sex marriage, which was legislated late last year.

In a pointed reference including some (unnamed) ministers who have criticised the judiciary, Brandis said he had not disguised his concerns at attacks on the institutions of the law – the courts and those who practised in them.

“To attack those institutions is to attack the rule of law itself. And it is for the attorney-general always to defend the rule of law – sometimes from political colleagues who fail to understand it, or are impatient of the limitations it may impose upon executive power – because although the attorney-general is a political official, as the first law officer he has a higher duty – a duty to the law itself.

"It is a duty which, as my cabinet colleagues know, on several robust occasions, I have always placed above political advantage.”

Brandis also was blunt in his rejection of those who want to see the government seek to inject more partisanship into national security.

He observed that eight tranches of national security legislation he had overseen were passed with opposition support after parliamentary committee scrutiny.

“It was a fine example of government and parliament working hand-in-hand to protect the national interest.

"I have heard some powerful voices argue that the Coalition should open a political front against the Labor Party on the issue of domestic national security.

"I could not disagree more strongly.

"One of the main reasons why the government has earned the confidence of the public on national security policy is that there has never been a credible suggestion that political motives have intruded.

"Were it to do so, confidence not just in the government’s handling of national security, but in the agencies themselves, would be damaged and their capacity to do their work compromised.

"Nothing could be more irresponsible than to hazard the safety of the public by creating a confected dispute for political advantage. To his credit, the prime minister has always resisted such entreaties.”

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.