The father of Britain's new Prime Minister said the EU was risking peace in Ireland by insisting on a Withdrawal Agreement "we can't agree to".
Stanley Johnson, who was a staunch remain campaigner ahead of the 2016 referendum, said leaving the EU without a deal would be "far worse" for Ireland if no alternative arrangements for the backstop were agreed upon.
"Who is throwing Ireland under a bus? It's not us. It's the EU by insisting on an agreement we can't agree to," he told talkRADIO's Julia Hartley-Brewer.
The Northern Ireland backstop would keep an open border between Northern Ireland and Ireland post-Brexit, and ensure no hard border, which would involve physical checks and infrastructure.
But Mr Johnson said the "failure of Europe to budge" on negotiating a new deal meant a no-deal Brexit must remain on the table, and with it, the possibility of a hard border.
"It is perfectly obvious that Boris and the cabinet he appoints wil be clear that no deal is the default option and that is where we go unless the Europeans move," he continued.
"The hopeful sign is that there are countries around the EU where our point of view is beginning to stick."
Boris Johnson has called for the backstop to be removed from Mrs May's withdrawal agreement, and instead included in the future relationship talks.
He called the backstop arrangement in his predecessor's deal a "monstrosity".