Former Taoiseach John Bruton has said the backstop to prevent a hard border in Ireland in the event of a no-deal Brexit will not be dropped.
Mr Bruton said that a vote by British Parliament on the backstop would be "like saying that an insurance company would be free to, at their own wish, negate the insurance policy".
"The backstop is only an insurance policy against the possibility that an agreement won't be reached," he told the BBC's Radio 4 Today programme.
"One suspects that those who object to the backstop are people who don't really expect there ever will be an acceptable agreement which would avoid a hard border in Ireland or between Ireland and Britain," he said.
In the event that no deal is reached by the March 29 deadline, Mr Bruton said that under EU law, there will be a hard border on the island of Ireland.
He agreed that unless a compromise is reached on Theresa May's Brexit deal, Britain is heading towards a no-deal exit from the EU.
The former Fine Gael politician served as Taoiseach from 1994 to 1997 and during a key time for the peace process in Northern Ireland.
Mr Bruton stressed the importance of safeguarding the Good Friday Agreement and to ensure that neither nationalist nor unionist communities in Northern Ireland are isolated.
"We changed our Constitution, and took certain articles out of our Constitution, in return for an international commitment from Britain to the Belfast Agreement which guaranteed fair treatment of both communities in Northern Ireland, that neither community would be isolated," he said.
"We changed our Constitution to make that deal and then Britain comes along unilaterally and essentially decides to tear that up in proceeding with Brexit.
Commenting on reports that the Northern Ireland Secretary, Karen Bradley, warned that a poll on a united Ireland would be more likely in the event of a no-deal Brexit, Mr Bruton said there was "no great threat" of this.
"I think the Union is secure because the Belfast Agreement says clearly that Northern Ireland will remain part of the United Kingdom unless and until, by a free majority decision, the population in Northern Ireland decide to change that and I don't think that's going to happen in the near future.
"I certainly don't think that we should make a big change like that in a referendum on the basis of 52% to 48% majority because we have seen with Brexit how divisive that can be," he said.
When asked his view on Sinn Féin MPs not taking their seats in Westminster, Mr Bruton said the party's record was "extremely bad".
There are currently seven elected MPs who refuse to attend Parliament.
"Sinn Féin have refused to take their seats on this occasion, and the most serious threats to the position of Northern nationalists are now about to be realised with no Sinn Féin, no Northern nationalist voice there to argue a different case.
"I think it's a great shame, it's a tragedy," he said.
Meanwhile, Sinn Féin will host an event to commemorate the 100th anniversary of the first Dáil in Dublin later today.