In an op-ed piece published in 20 European newspapers last week, EU chief Brexit negotiator Michel Barnier opined that Theresa May's latest Brexit proposal threatens the future of the EU single market.

Quoting from M. Barnier's op-ed piece:

"Let's be frank: as the UK has decided to leave the Single Market, it can no longer be as close economically to the rest of the EU. The UK wants to leave our common regulatory area, where people, goods, services and capital move freely across national borders. These are the economic foundations on which the EU was built. And the European Council – the 27 Heads of State or government – as well as the European Parliament have often recalled that these economic foundations cannot be weakened.

"The UK knows well the benefits of the Single Market. It has contributed to shaping our rules over the last 45 years. And yet, some UK proposals would undermine our Single Market which is one of the EU's biggest achievements. The UK wants to keep free movement of goods between us, but not of people and services. And it proposes to apply EU customs rules without being part of the EU's legal order. Thus, the UK wants to take back sovereignty and control of its own laws, which we respect, but it cannot ask the EU to lose control of its borders and laws."

In his article M. Barnier also reiterated his concern regarding the Ireland-NI border - a critical issue for tourism in both countries:

"The biggest risk caused by Brexit is on the island of Ireland. We need to make sure that Brexit does not create a hard border between Ireland and Northern Ireland, and that the Good Friday Agreement, which has brought peace and stability to Northern Ireland, will be protected. Today, the cooperation and exchanges between Ireland and Northern Ireland occur within the common framework of the EU. Since we will not know what the future relationship will bring by Autumn 2018, we need to have a "backstop" solution in the Withdrawal Agreement. The UK agrees with this, and both the EU and the UK have said that a better solution in the future relationship could replace the backstop. What the EU has proposed is that Northern Ireland remains in a common regulatory area for goods and customs with the rest of the EU. We are ready to improve the text of our proposal with the UK."

It's widely speculated that if Brexit occurs with a "temporary" backstop provision in place, that provision could remain in effect indefinitely.

So let's get it right the first time.