Taoiseach Leo Varadkar arrives at an informal European Union summit with Western Balkans countries at the National Palace of Culture in Sofia, Bulgaria. Photograph: Vassil Donev/EPA

Ahead of a meeting with British prime minister Theresa May in Sofia, Bulgaria, Taoiseach Leo Varadkar has warned that Britain’s Withdrawal Agreement with the EU could be in question if progress is not made in Brexit talks by next month.

Taoiseach Leo Varadkar has warned that Britain’s Withdrawal Agreement with the European Union could be in question if progress is not made in Brexit talks by next month.

Mr Varadkar will meet British prime minister Theresa May on Thursday on the fringes of the EU’s Western Balkans summit in the Bulgarian capital Sofia.

Speaking to journalists at the beginning of the meeting, the Taoiseach said: “If we are not making real and substantial progress by June then we need to seriously question whether were going to have a Withdrawal Agreement at all.

“We stand by the text of the Withdrawal Agreement and the text of the protocol published in March as does the task force and the 27 member states that are behind us, ” Mr Varadkar said.

Black and white “But we need to see it written down in black and white and know that it is workable and legally operable. And we’ve yet to see anything that remotely approaches that.”

Asked about protecting Irish businesses from US sanctions over trading with Iran, he said EU leaders were demanding a permanent exemption for European businesses in the wake of its repudiation of the nuclear deal.

Although he demurred when asked to endorse European Council president Tusk’s comments about US president Donald Trump - that “with friends like that who needs enemies” - he strongly supported the continued application of the Iran nuclear deal

“I’m not sure that I would use exactly those words. In Ireland and I’m sure its the case that across Europe we’ve always considered the US to be friends and partners.

“However there are growing differences on issues like trade and the status of Jerusalem and also on Iran.” He said EU leaders gave very strong support to Mrs May, German Chancellor Angela Merkel, and French president Emmanuel Macron at an informal dinner on Wednesday to continue to support the Iran deal.

“The deal isn’t perfect but it has worked and we made that agreement with Iran and I believe we should stand by it.”