Legal challengers attempting to give parliament the authority to trigger Brexit have a wider aim of trying to invalidate the referendum result, the attorney general, Jeremy Wright QC, has told the high court.

Opening the government’s response to the constitutional claim, Wright declared that the making and unmaking of international treaties was a recognised use of the royal prerogative – executive powers available to the government.

The legal dispute is over whether parliament or ministers have the authority to formally notify Brussels that Britain is withdrawing under article 50 of the treaty on European Union (TEU).

Article 50 states that any member state may leave “in accordance with its own constitutional requirements”, an undefined term that has allowed both sides to pursue rival interpretations.

Three of the most senior judges – the lord chief justice, Lord Thomas of Cwmgiedd, the master of the rolls, Sir Terence Etherton, and Lord Justice Sales – are hearing the challenge, which could have far-reaching political and constitutional consequences.

The attorney general, who is leading the government’s legal team, told the court on Monday: “This is not a narrow legal challenge … It seeks to invalidate the decision already taken to withdraw from the EU.

“Making and unmaking treaties are an established use of royal prerogative powers. The use of prerogative powers [to trigger Brexit] was wholly within the expectation of parliament.

“The question is, has parliament acted to limit the availability of the royal prerogative powers? The answer, we say, is no.

“There’s nothing expressed in legislation that [shows] parliament has attempted to circumscribe the powers to make treaties. Parliament has conspicuously refused to legislate on withdrawing from the EU despite many opportunities if it had so wanted.”

Wright urged the court not to be distracted by the question of whether formal notification of the UK’s intention to leave under article 50 could be reversed once given.

“We do not argue that once article 50 [notification has been given] it can be revoked,” Wright said. “We ask the court to proceed on the basis that it’s irrevocable.

“[The government] is also content that, as a matter of firm policy, [that] notification of withdrawal will not in fact be withdrawn.”

Wright added: “The other parties in this case have sought to say they are defending the sovereignty of parliament. We say that parliament can retain its sovereignty as much by choosing not to do something as by doing something.

“It chose not to restrict the way royal prerogative powers work on multiple opportunities.

“The prerogative powers are available to use, we say, to give clear effect to the wishes of the people of the UK that we should begin the process of leaving the EU.”

James Eadie QC, who is also representing the government, said that giving notice under article 50 “would not have any immediate effect on UK law”.

Parliament would still be involved in the withdrawal process as it developed, he added. “The claimants have greatly exaggerated the impact on domestic rights that withdrawal from the EU will have.”

The case has profound constitutional and political implications, Eadie admitted. It tests the “flexibility” of the UK’s constitution. “We are dealing here with exceptional and probably unique circumstances. There’s no written constitutional formula.”

The consequence of the claimants’ case, Eadie asserted, was “to deny the constitutional flexibility which lies at the heart of our arrangement”. Parliament had, by design, left certain powers in the hands of the government.

But Etherton, the master of the rolls, asked whether the fact that parliament had not specified the precise limits of the royal prerogative meant that “the government can remove common law rights?”

And the lord chief justice enquired whether it was permissible to rely on the royal prerogative to withdraw from a treaty “even if it has effects on domestic law rights?”

The case continues.