Stark divisions over Brexit and the future of the Irish Border were evident at an EU summit in Salzburg last night as British prime minister Theresa May told fellow leaders that a border on the Irish Sea was “simply not acceptable” to her.

Taoiseach Leo Varadkar told reporters that no progress had been made on the backstop since March and that the Government was making preparations for a no-deal outcome in the talks on the UK’s departure from the bloc.

“I don’t think anyone wants to contemplate a no-deal scenario,” he said. “I don’t believe a no-deal scenario is where we’re heading but certainly Ireland is prepared for it.

“We’ve already started the process of hiring hundreds of people to staff our ports and airports. We’ve already started to approve the IT system, the infrastructure that may need to go into place. I want to emphasise that’s in the ports and airports for east/west trade. We’re not making any preparations for a hard border.”

Ahead of the dinner, sources said Ms May would tell her fellow leaders that: “It has been clear from the outset that we can never accept a border on the Irish Sea. . . A customs border would undermine our constitutional position.”

She was also expected to say that “the commission is proposing I should assent to legal separation of the UK into two customs territories. That is simply not acceptable”.

‘De-dramatise’

This was seen as a response to attempts by the chief EU negotiator Michel Barnier to “de-dramatise” the issue of controls on the Irish Sea in the event of Northern Ireland remaining part of the customs union and single market after Brexit.

Mr Barnier has insisted in recent weeks that such controls need not take place on the Border or be seen as a border, or have any implications for the constitutional status of Northern Ireland.

Ms May was having none of it, with sources saying she remained solidly committed to the British pledge in December to a “backstop” for Northern Ireland, which both sides differ sharply on the shape of.

Sources close to the prime minister accepted, however, that London would be bringing forward proposals on the regulatory control dimension of their backstop proposals and did not rule out that some such controls could be carried out in the Irish Sea.

On the overall deal Ms May was expected to reiterate her commitment to getting agreement.

“We have a shared history, and shared challenges . . . and we have a desire for a shared future,” she said. “The onus is on all of us to get this deal done.”

There were no responses at the dinner to Ms May’s speech, which will be discussed by the 27 remaining states at their lunch today after she leaves Salzburg. Ms May and Mr Varadkar will hold a bi-lateral meeting this morning.