THERESA May has indicated she is looking at the customs arrangements between the US and Canada as a way of solving the Irish border issue after Brexit.
But the prime minister was immediately mocked at Westminster over the comparison - with one MP telling her the US-Canada frontier has armed guards - and taoiseach Leo Varadkar also said it was definitely not an option.
Mrs May had said: "There are many examples of different arrangements for customs around the rest of the world.
"Indeed we are looking at those, including for example the border between the United States and Canada."
When it was later pointed out by shadow Brexit minister Jenny Chapman that there were "armed customs guards", Mrs May said the government was looking at arrangements "in a number of countries".
She again told MPs there would be no return to a hard border in Ireland.
She has rejected Brussels proposals that would see the north kept in an effective customs union with the EU as a fall-back if other solutions cannot be found.
"As prime minister I am not going to let our departure from the EU do anything to set back the historic progress made in Northern Ireland," she said.
"Nor will I allow anything that would damage the integrity of our precious union.
"The UK and Irish governments and the European Commission will be working together to ensure that we fulfil these commitments."
Labour leader Jeremy Corbyn said Mrs May offered "no real solution" over the border, and instead "rehashed an already discredited government idea" to use a mix of technology and goodwill.
He said: "Doesn't the prime minister understand, this isn't just about cross-border paperwork and trade - there is also an issue of maintaining the social peace that has endured for 20 years."
He also asked Mrs May to condemn foreign secretary Boris Johnson's "ridiculous remarks" over the border, he claimed the issue was "being used" to stop Brexit.
Mr Varadkar later said he had not heard the prime minister's comments so he did not want to comment directly, he did discuss a trip to the US-Canada border.
"I visited the US-Canada border, I visited it back in August, and I saw a hard border with physical infrastructure, with customs posts, people in uniforms with arms and dogs and that is definitely not a solution that is one that we can possibly entertain," he aid.
Meanwhile, a former Tory cabinet minister who was caught up in the Brighton bomb has criticised "extreme Brexiteers" over comments about the Good Friday Agreement.
John Gummer, who sits in the House of Lords as Lord Deben, said: "I've rarely been as angry as I was when I saw those extreme Brexiteers who tried to ridicule the Good Friday Agreement as if it didn't matter.
"I say that as somebody who was in the Brighton bombing, whose wife was in the Brighton bomb, who had to help pick the things up afterwards."
