There will be a border in the Irish Sea under the Brexit deal negotiated by Boris Johnson, the EU's chief negotiator has said.
Michel Barnier confirmed there would be "checks and controls" between Britain and Northern Ireland under the agreement that will govern the UK's exit from the EU.
Boris Johnson claimed several times during the general election campaign that there would be no checks on the Irish Sea, and was accused by the Opposition of lying.
Whether the Prime Minister had misunderstood the agreement he had signed, or was indeed lying to the public, the text of the deal signed in November is clear that there will indeed be checks.
"The implementation of this foresees checks and controls entering the island of Ireland," Mr Barnier said during a sitting of the European Parliament. "I look forward to constructive co-operation with British authorities to ensure that all provisions are respected and made operational."
Mr Barnier had kept quiet during the UK general election campaign, telling anyone who asked him - even in private - that he did not want to say anything that could have political impact and undermine his Brexit deal.
Mr Johnson repeated his claim just on Monday, telling a Press conference: "Be in no doubt. We are the Government of the United Kingdom. I cannot see any circumstances whatever in which there will be any need for checks on goods going from Northern Ireland to GB.
"The only circumstances in which you could imagine the need for checks coming from GB to NI, as I've explained before, is if those goods were going on into Ireland and we had not secured, which I hope and I'm confident we will, a zero tariff, zero quota agreement with our friends and partners in the EU."
During the election he was even more emphatic, saying: "We will make sure that businesses face no extra costs and no checks for stuff being exported from NI to GB."
But his analysis does not accurately reflect what is in the Brexit deal he signed.
The Government's own internal analysis, leaked during the general election campaign, said there would be checks on goods in both directions.
It also said there would be a devastating impact on the Northern Ireland economy and claimed 98% of Northern Ireland export businesses would be "likely to struggle to bear this cost" of customs declarations and documentary and physical checks on goods within the UK.
The DUP's Westminster leader Sir Jeffrey Donaldson last night dismissed Mr Barnier's comments as "typical of his continual attempts to undermine Brexit".
He said: "Michel Barnier should take time to read the recent agreement that has been reached in which the UK Government has committed to introduce measures that will mitigate the impact of the arrangements for Northern Ireland post-Brexit.
"The EU withdrawal agreement actually states that Northern Ireland businesses should have unfettered access to the UK single market and we are determined to ensure that is the case."
The Lagan Valley MP added: "These comments are designed to be unhelpful and Michel Barnier should now focus on negotiating the future relationship rather than trying to cause problems with the withdrawal arrangements.
"He should accept that Brexit is happening and it's now time for the EU to get down to the business of agreeing a new free trade agreement. In the end the internal UK market will be a matter for the UK Government post-Brexit.
"When you consider that all the Northern Ireland parties and business leaders have united in calling on the UK Government to introduce the measures that they are now committed to, I think that shows where the impetus is in all of this.
"Talk of border checks are out of tune with what both Northern Ireland businesses and political parties want to see."