Frictionless trade after Brexit will be impossible, the EU chief Brexit negotiator has said.
Michel Barnier made the comments to an audience at the Queen’s University in Belfast just days before the UK is set to leave the EU.
“The UK has chosen to become a third country; to leave the Single Market and the Customs Union; to leave behind the EU’s framework of common rules, common supervision and common Court of Justice,” Mr Barnier said.
“It has chosen to create two regulatory spaces. This makes frictionless trade impossible. It makes checks indispensable.”
Mr Barnier said Northern Ireland "will be the part of the UK most impacted by Brexit", due to its "specific constitutional and legal set-up both in terms of governance and in terms of co-operation across Ireland".
He said the Stormont Assembly - which had been defunct for three years until earlier this month - "had been missed during the negotiations on Brexit and Northern Ireland".
"Although I met with Northern Ireland's leaders many times in the few years, the requests were always to meet separately, with one party. Never to meet together," he said.
"This afternoon, I met with Sinn Féin's deputy First Minister, Michelle O'Neill, together with the DUP's Economy Minister, Diane Dodds, representing the First Minister, Arlene Foster. "So I am very glad to see the Legislative Assembly restored."
Mr Barnier said the EU had worked "tirelessly" to find a deal to meet Irish, Northern Irish and British concerns.
He said the EU had showed "flexibility and understanding" last summer when Prime Minister Boris Johnson asked for the backstop to be abandoned.
"The protocol on Ireland and Northern Ireland that we have agreed on is indeed complex but operational," he said.
"It allows Northern Ireland to remain in the UK customs territory and, at the same time, benefit from access to the Single Market without tariffs, quotas, checks or controls.
"The protocol is not an insurance policy, but a workable system, built to last. And, importantly, it gives the elected representatives of Northern Ireland's legislative Assembly the right to decide whether to continue applying the system or not, four years after it starts to apply.
"I look forward to Northern Ireland's Executive playing a stronger role on this matter, now that it is up and running."
Speaking to politicians including former Irish premier Bertie Ahern as well as business and community leaders, Mr Barnier confirmed checks will take place.
“We will need sanitary and phyto-sanitary checks on food products and live animals,” he said.
“The EU must be able to assess risks on any product coming into its market and, if necessary, activate physical controls.
“These checks must take place somewhere.
“And as the whole point of the protocol is to avoid a hard border and protect the all-island economy, it was clear that they could not take place at the land border between Ireland and Northern Ireland.
“The only real option was to use Northern Ireland’s other entry points. This is also where such checks are the easiest to implement. And controls will also take place in Dublin and other EU entry points.”
Mr Barnier said negotiating the future partnership between the EU and UK is "another huge challenge", adding that 11 months is an "extremely short" period of time.
"Prime Minister Johnson has said he will not extend this period. This means that the UK will leave the Single Market at the end of this year. This is the UK's choice. We respect it. And we will do everything we can in the short time that this makes available," he said.
Earlier he met with Taoiseach Leo Varadkar at Government Buildings in Dublin, where he insisted any change in government would not have any impact on his working relationship with Ireland.
“Obviously I have been informed of the next election in this country.
“Frankly speaking, as an EU negotiator I always worked with each and every other 27 EU member state with elected governments,” he said.
“I will continue to work with the government chosen by the citizens.”
The latest poll shows that Fianna Fáil remains in the lead to be the majority partner in the next government and not the current holders Fine Gael.