Sir Vince Cable MP has said two decades of work for peace in Northern Ireland will be completely wasted if the Government fails to get it right with Brexit.
The ongoing withdrawal from the European Union has raised the question of what will happen on the Irish border.
The border between Northern Ireland and the Republic is the only land barrier the UK shares with any other EU member-state.
Cable, the leader of the Liberal Democrats and MP for Twickenham, told James Whale the installation of a type of "Berlin Wall" in Ireland would be "unacceptable."
He said: "Most people would accept it would be intolerable, after all the efforts made to create peace in Northern Ireland, that we now built a type of Berlin wall across the island of Ireland.
"Unless we get this right, then two decades of hard work by successive governments will go to waste.
"We’ll be back to confrontation and the sectarianism that poisoned Northern Ireland for a long time.
"The best [option] is we simply don’t go there at all."