The EU is claiming Northern Ireland ports are being used to smuggle counterfeit goods into the single market, Brussels has claimed.
Several large-scale smuggling incidents show that EU concerns over the operation of the Northern Ireland Protocol are not theoretical, it added.
Seizure of counterfeit high-value electrical products last year, fitted with the European Union-type plugs, show the need for robust processes at Northern Ireland ports, an EU official told the PA news agency.
The official said there was evidence criminals were trying to use the Irish Sea crossing to get prohibited products into the EU single market.
Drugs and weapons have also been seized, they added.
"There is smuggling going on, for sure," they added.
The EU official said the ongoing failure by the UK to provide real-time data on trade movements in a useable format meant the EU was unclear "how big the problem is" in relation to smuggling.
However, the official said seizures made by UK Border Force, with the involvement of EU personnel on the ground, have indicated it was a significant issue.
"In March 2021, there was a seizure of undervalued and counterfeit high-value electronic products such as smartphones sent in parcels, plugs were EU type,” said the official.
"Between April and May 2021 and in October 2021 there were seizures of smartphones including counterfeit ones, tobacco, cigarettes, weapons, drugs and medicines hidden in parcels.
"In December 2021, in the context of control on postal deposits, there were seizures of heroin, cocaine, cannabis, 177,000 prescription medicine tablets, 24 kilos of tobacco, nearly 17,000 cigarettes.
"So, this is not theory."
The claims come as a row between the EU and UK government over the Northern Ireland protocol deepens, as the union accuses Boris Johnson's government of 'breaking the law'.
The EU has resumed legal action in retaliation over the Prime Minister’s plans to unilaterally scrap parts of the protocol, after agreeing the Brexit deal.
Foreign secretary Liz Truss has insisted the changes the UK government is set to make to the protocol do not breaking the law, adding that there is no need for legal action.
European Commission vice-president Maros Sefcovic said the UK’s move had “no legal or political justification”.
As well as new legal action for alleged failures to implement the protocol as it stands, Mr Sefcovic confirmed that existing infringement proceedings which had been paused while UK-EU talks took place would now be resumed.
And he indicated further measures could follow if the UK pressed ahead with the Northern Ireland Protocol Bill, which will effectively rip up key parts of the deal signed by Mr Johnson and the EU in 2019.
A UK Government spokesman said on Wednesday (15 June): “It is disappointing that the EU has chosen to relaunch legal proceedings relating to the grace periods currently in place, which are vital to stop the problems caused by the protocol from getting worse.
“The UK’s preference remains for a negotiated solution but the proposals set out by the EU today are the same proposals we have been discussing for months and would not solve the problems – in many cases they take us backwards from current arrangements.”
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