GLENTIES: Irish Prime Minister Leo Varadkar said on Friday he would need to meet his British counterpart Boris Johnson to understand his "real red lines" on Brexit, and that Ireland had shown in the past that it could be flexible.

Varadkar's deputy Simon Coveney had earlier said Johnson's approach to Brexit was "very unhelpful" and that he appeared set on a collision course with the European Union that would preclude an orderly exit with a transition deal.

"What I would like to do when I get a chance to speak to him is to get a sense from him as to what he is thinking and what his plans are. He has demonstrated a degree of flexibility in the past," Varadkar told a politics forum, joking that Johnson had voted both for and against the Withdrawal Agreement his predecessor Theresa May negotiated with the EU.

"Dealing with counterparts, you only really get a sense of where they are going and what their real red lines are if you are in ... a one-on-one meeting," he said.

Varadkar said Johnson was taking "a much harder-line position" than May had done, in particular by calling for the scrapping of the Irish border backstop -- Ireland's own main red line in the talks.

The backstop aims to ensure EU member Ireland's now-invisible border with the British province of Northern Ireland remains open but some British politicians fear it could tie the United Kingdom into the EU's customs union indefinitely.

Ireland says any checks or border infrastructure could undermine the 1998 peace deal that ended a three-decade conflict in Northern Ireland between pro-British unionists and Irish nationalists in which more than 3,600 people died.

Varadkar said he took comfort in the fact that Johnson says he wants a deal -- something the Irish premier said would clearly require the backstop.

"If he means what he says about wanting to leave with a deal and wanting a free trade agreement with the European Union, then he will have to depart from some of what he has said in the last couple of days," Varadkar said.

"Let's see what he says in a few weeks' time. This is the way politics is done sometimes."

Varadkar said Ireland and the EU had shown flexibility in the past by accepting a review clause on the backstop and extending the backstop to cover the whole of the United Kingdom.

"We are not reopening the withdrawal agreement ... but we have shown reasonableness and flexibility in the past."

But the backstop was not negotiable, Varadkar said: "A Withdrawal Agreement without a backstop is the same as no-deal."