Brian Hayes, MEP for Dublin, said some progress was being made in Brexit negotiations but the Republic of Ireland should still prepare for a catastrophic no deal scenario.
He said the Irish border issue was an immovable roadblock for Britain, who remained unable – or unwilling – to appreciate the scale of the problem.
The Irish border, despite increasingly frustrated pre-referendum warnings from Dublin, Belfast and Brussels, has become the inevitable Catch 22 issue of Brexit talks.
Prime Minister Theresa May and her Brexit ministers have repeatedly vowed to avoid a hard border after Brexit, with Dublin refusing to entertain the prospect of passport or customs checks or any form of physical infrastructure
But after Brexit the border between the Republic of Ireland and Northern Ireland will become the UK’s only land border with the EU, with Mrs May under pressure to deliver on promises to end free movement and regain control of Britain’s borders.
Mr Hayes has now warned the problem may never be solved, resulting in a breakdown in talks between Brussels and Westminster.
The MEP wrote on his blog: “The Irish border issue could still derail these talks.
“The prospect of a failure of the talks come October, or a rejection of the agreement by the UK Parliament, cannot be underestimated.
“The British political system is still in deep crisis and the UK government cannot seem to produce any sensible policy proposals.
“It is not the job of the Irish government to solve domestic British politics but we can help to soothe relations between the EU and the UK as we get to the crunch trade talks.”
He said it was time for Ireland to stand up and be counted in negotiations or face an economic crisis.
Mr Hayes said: “It is time now to really start focusing our efforts on the East West issues between Ireland and the UK. With about €1.2 Billion worth of trade carried out across the Irish Sea every week, we have so much at stake here.
“A deep and comprehensive trade deal between the EU and UK is the big prize at the end of Brexit. This would resolve the great majority of Ireland’s issues in relation to the border and the overall trading relationship with the UK.
“As the negotiations get going on the future relationship, Ireland has a role to play in helping to build bridges and facilitate a willingness to work towards a comprehensive free trade agreement.”