LONDON - The favourite to become Britain’s next prime minister, Boris Johnson, has raised the Brexit stakes by saying he will discard a contentious part of the European Union divorce deal agreed by outgoing leader Theresa May.

Britain’s Parliament rejected May’s deal, in large part because of a measure designed to ensure an open border between the U.K.’s Northern Ireland and EU member Ireland.

Brexit supporters think the so-called “backstop” keeps Britain too closely bound to EU trade rules. Some have argued for an exit clause or time limit.

But during a leadership debate Monday, Johnson rejected “time limits or unilateral escape hatches or all these elaborate devices.”

EU leaders say there can be no withdrawal agreement without the backstop.

Johnson’s stance appears to heighten the chance of a disruptive “no-deal” Brexit.