The Government endured bruising attacks from across the House as it moved to scrub an entrenchment clause from its Three Waters legislation, with the Prime Minister saying it was a “mistake” to include it in the first place.

Labour and the Greens entrenched anti-privatisation provisions in the Three Waters bill. Those measures were removed after the bill was referred back to the Committee of the Whole House stage on Tuesday afternoon.

National’s shadow leader of the house Chris Bishop said the episode had echoes of Muldoon-era constitutional impropriety, including the famous Fitzgerald v Muldoon. That case found the then Government to have broken the law by suspending the operations of superannuation legislation without the consent of Parliament.

Attorney-General David Parker said the comparison was an “exaggeration”.

 “On that occasion the prime minister broke the law - no law has been broken here,” Parker said.

Constitutional law experts warned that entrenching a matter of policy was potentially dangerous, and opened the door to tit-for-tat entrenchment of policy which would undermine the sovereignty of Parliament, or undermine the efficacy of entrenchment altogether.

The question has now moved to whether Labour MPs are correct in saying the entrenchment was a mistake, as claimed, or whether at least some MPs knew what they were doing. That question has been directed at Local Government Minister Nanaia Mahuta, who was in the chamber for the debate.

 “My question for the minister is a really simple one: what on earth were you thinking? What on earth possessed the Government to think this was appropriate or constitutional,” Bishop said.

He compared the imbroglio to a famous Spiderman cartoon in which multiple people dressed as Spidermen point to each other, each trying to ascertain who is the real Spiderman. Bishop had earlier Tweeted a version of this metaphor.

“What we have at the moment is like that Spiderman cartoon, everyone in the Government pointing to everybody else and saying they’re to blame: Jacinda Ardern says it’s Nanaia Mahuta’s fault, Nanaia Mahuta says ‘nothing to do with me I’m blaming the Finance and Expenditure Committee’, David Parker says ‘I’ve always been opposed to entrenchment’,” Bishop said.

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National’s deputy leader Nicola Willis described the effort to scrub the entrenchment clause as a “grovelling backdown”.

“The stain on our country and the damage to our constitution will remain,” Willis said.

Parker said he agreed “with some of the comments that have been made by the opposition”.

“I agree and the Government agrees that the entrenchment of the anti-privatisation clause is an inappropriate use of the entrenchment tool, which is why we have brought the amendment back to the House today,” Parker said.

Parker said he could understand why some MPs in Labour were attracted to the idea, but said he had always opposed it.

“There are very limited use of entrenchment provisions in respect of constitutional norms that are long settled. It is very important that we keep it that narrow for a number of reasons.

“This Parliament cannot bind a subsequent parliament ... it is the right of a subsequent parliament to change the law,” he said.

Act MP Simon Court asked Mahuta what she actually meant by privatisation, and whether the scope of this term included things like private capital. All Three Waters proposals currently include the need for private capital.

Green MP Eugenie Sage, who proposed the amendment in the first instance, stood by it.

She said in the debate that National had “privatisation on its mind”.

“National is not engaging with the substance of what their views are about the future of Three Waters assets,” Sage said.