The European Union has told Britain there are still too many unanswered questions over Brexit, increasing the pressure on Prime Minister Theresa May as she tries to unite her government over plans to leave the bloc.

As the EU’s chief Brexit negotiator Michel Barnier warned that time was running out, May convened what were expected to be marathon talks on Friday at her Chequers country residence to agree on a plan for Britain’s future outside the EU.

After months of reticence, May has been forced to thrash out an agreement with her divided cabinet of ministers to push on with all-but-stalled talks and ease growing concerns about a no-deal Brexit.

But the first details of May’s new plan for close customs ties with the EU – a “facilitated customs arrangement” – won mixed reviews, with Brexit campaigners saying she was offering the country a Brexit in name only.

And in Brussels, Barnier said much work remained to be done.

“In the Brexit negotiations, there are still too many questions and too few answers,” Barnier said.