Brexit minister Lord Frost has accused the EU of being an organisation “that doesn’t always look like” it wants the UK to succeed as he demanded changes to post-Brexit arrangements for Northern Ireland.

In a speech in Lisbon, the cabinet minister called on Brussels to help “tackle the fundamental issues” with the Northern Ireland Protocol – which he claimed was “not working” – and to show “the same ambition and willingness” to solve problems.

He also reiterated a threat to suspend post-Brexit arrangements for Northern Ireland by triggering Article 16 of the Protocol.

But critics attacked Lord Frost for now trashing an agreement he helped negotiate with Prime Minister Boris Johnson less than two years ago, and for risking a new row with the EU.

In his speech on Tuesday, Lord Frost said the Protocol was “the biggest source of mistrust” between the EU and UK and said the border arrangements had “completely lost consent in one community in Northern Ireland”.

“There is a widespread feeling in the UK that the EU did try to use Northern Ireland to encourage UK political forces to reverse the referendum result or at least to keep us closely aligned with the EU,” he added.

“And, moreover, that the Protocol represents a moment of EU overreach when the UK’s negotiating hand was tied, and therefore cannot reasonably last in its current form.

“Whether or not you agree with either analysis – the facts on the ground are what matter above all.

“Maybe there is a world in which the Protocol could have worked, more sensitively implemented.

“But the situation has now moved on. We now face a very serious situation. The Protocol is not working.”

Lord Frost revealed he had shared a new legal text with the European Commission on Tuesday with his planned changes for the Protocol.

These include the removal of the European Court of Justice (ECJ) from oversight of the Protocol.

He spoke ahead of EU vice-president Maros Sefcovic delivering Brussels’ response on Wednesday to the UK government’s suggested changes to the Protocol, which Lord Frost outlined in July.

The Brexit minister said the UK was “really ready” to discuss the EU’s own proposals “whatever they say and we will obviously consider them seriously, fully, and positively”.

But he warned the EU must be ready to agree to “significant change” to the Protocol.

“We need the EU to show the same ambition and willingness – to tackle the fundamental issues at the heart of the Protocol head on,” Lord Frost added.

Senior EU figures – including French President Emmanuel Macron – have previously warned that “nothing is negotiable” with regards to the Protocol.

But, while Lord Frost admitted he understood why the EU “feels it is difficult to come back to an agreement reached only two years ago”, he stressed “that in itself is far from unusual in international relations”.

Responding to Lord Frost’s speech, former Conservative minister Gavin Barwell – who was also chief of staff to ex-prime minister Theresa May – accused the Brexit minister of causing new tensions with EU nations.

“The absolute state of David Frost trashing the deal he negotiated + hailed as a triumph – despite many, yours truly included, warning it was a dud – *and worse* now using it to further undermine our relationship with some of our closest friends in an increasingly dangerous world,” he posted on Twitter.

Labour’s shadow Brexit minister, Baroness Chapman, claimed senior Conservatives were “desperate to use a tussle with Brussels to distract from their domestic failures – whether on COVID, the energy crisis, or the needless culling of thousands of pigs”.

She added: “Today was an opportunity for the government to reset relations with our partners in the EU after a fractious start to our new relationship.

“Instead of approaching the occasion with maturity and in the spirit of cooperation, Lord Frost has effectively asked to rip up the agreement he negotiated – and the Prime Minister signed – just two years ago.”

And Liberal Democrat MP Alistair Carmichael, the party’s Northern Ireland spokesperson, said: “This Conservative government is playing out like a badly-written farce.

“The same minister who just months ago was trumpeting the government’s botched Brexit deal now says it’s intolerable and has to be changed.

“After all the upheaval British businesses have suffered and all the challenges they face now, they need certainty and support from the government, not more pointless posturing.”