Belfast is not constitutionally the same as Finchley, the former Irish prime minister who sealed the Good Friday agreement for Northern Ireland, has said.

Bertie Ahern told MPs the problem with the Brexit impasse was that people believed Northern Ireland was exactly the same as Scotland, Wales or England in its position within the UK.

“The argument that … Northern Ireland is precisely the same as Finchley is incorrect, it’s constitutionally incorrect as per the Good Friday agreement and I think people need to understand that,” he told the Brexit select committee at the House of Commons on Wednesday.

“What does frustrate me and others is there is a view that Northern Ireland so still intrinsically linked to the UK in a way that ignores the Good Friday agreement and that’s the bit that really upsets us, because it is not.”

He said the “parity of esteem” enshrined in the three-stranded agreement was “absolutely paramount” to Northern Ireland and set it apart from the position of Scotland, Wales or England in the United Kingdom.

Ahern, along with Tony Blair, was one of the architects of the peace deal that led to referendums on both sides of the border and the removal of Ireland’s claim to the six counties in Northern Ireland that was part of the country’s founding constitution.

The former Fianna Fáil taoiseach admitted a no-deal Brexit could be “devastating” for “small indigenous farmers and small employers” but said voters would put the avoidance of a hard border over jobs and the economy.

Ahern was being pressed by the Brexiter MP Craig Mackinlay, the Conservative MP for South Thanet, over a recent report by Ireland’s central bank that a no-deal Brexit could reduce growth by up to 4% this year.

“I’m very surprised that there isn’t a fear factor creeping into the republic with all those losses of jobs, 4% reduction in GDP.

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“I’m surprised that it isn’t been addressed or the people of [the] republic aren’t saying, ‘come on government, you’re not actually reflecting our views here and get on with something different, have the flexibility the UK is looking for and we can get a deal over the line’,” said Mackinlay.

Ahern told him there was still hope a deal could be done, but Irish voters were supporting their government’s position.

“If you were to ask 1,000 Irish people can they conceive of any arrangement where they can go back to a hard border, that will take precedent,” he said.

Mackinlay told Ahern he was also puzzled about why there would be any need for a backstop when arrangements currently allowed the free flow of trade between Northern Ireland and the republic, despite differences in VAT, corporate tax and duties.

“The picture you well painted of how rosy the tree is, is exactly the reason you need a backstop, to keep it the way you painted,” replied Ahern to laughter.

“I’m afraid even as a good Brexiter you’ve made the argument for the backstop.”

Ahern was also asked how the notion of Ireland quitting the EU to break the Brexit logjam was going down at home. He responded: “I’ll just be kind and say ‘not very well’.”