Human Rights Commission president Gillian Triggs has told a ceremony marking the anniversary of Magna Carta that Federal Government "overreach" is eroding Australia's political system.

During a special sitting of the ACT Supreme Court, Professor Triggs said the Abbott Government's counter-terrorism laws and increasing powers of indefinite detention without judicial oversight were examples of this.

Professor Triggs paid tribute to the principles of law established in Magna Carta, which she described as a revolution in which the people desired to master a king.

Magna Carta was sealed in 1215 after a deal was struck to avoid a civil war in England over exorbitant taxes.

It reined in the power of King John, and while the first draft only lasted nine weeks, the principles laid the foundation of the modern rule of law.

Professor Triggs said its presence was felt down the centuries and formed the foundation for legal systems in Europe and even later in United Nations' conventions, including the Universal Declaration of Human Rights.

'Separation of powers doctrine being distorted'

But she said in Australia, some of this has been eroded, with a decline in the powers of Parliament and the courts as executive discretion expanded.

"Prioritised government power has become routine," she said.

"The separation of powers doctrine is becoming distorted."

Human Right Commission president Gillian Triggs (centre), with the ACT's Supreme Court judges, at the Magna Carta anniversary. ( ABC News: Adam Wyatt )

Professor Triggs said potential remedies included a Bill of Rights.

But she said as things stood currently, "the idea of a fair go ... is as close to a bill of rights as we are likely to get."

Professor Triggs stood firm despite increasing pressure for her to resign, after the Government said it had lost confidence in her over a report on children in detention.

Prime Minister Tony Abbott labelled it a "partisan stitch-up".

Tensions flared again this month, after she linked the Government's policy of boat turn-backs to Indonesia's lack of engagement on the broader death penalty issue.

Australians prefer 'the vibe' to 'the myth'

Meanwhile, ACT Supreme Court Justice Richard Refshauge borrowed from the iconic Australian film The Castle to explain the relevance of Magna Carta to modern law during the special sitting of the court.

Justice Refshauge said the ideas behind the document endured.

"So Magna Carta came to stand for the rule of law, limits on authoritarian rule, government subject to law and the rights and liberties of citizens," he said.

Justice Refshauge said most of the actual chapters of the document have long since gone.

"We Australians, with our no-nonsense and iconoclastic approach to life and, perhaps, the law, probably prefer 'the vibe' to 'the myth'," he said.

But he warned the rights and freedoms were not necessarily secure.

"They require constant protection and support," he said.

"As the eminent jurist Sir William Blackstone commented centuries ago, 'the body of the charter has unfortunately been gnawn by rats'.

"We must not let our fears, our alienation, our selfishness, our xenophobia, or our smugness allow our leaders to take up the task that the rats left unfinished."