BORIS Johnson has hit out at European leaders for failing to agree that the UK is “a single country”.

The Prime Minister told EU chiefs to “get that into their heads” as he ramped up with rhetoric in an increasingly bitter row over post-Brexit trading arrangements.

The Tory leader met European leaders in the margins in the G7 summit as wrangling over the Northern Ireland Protocol threatened to overshadow his hosting of the international gathering.

While Downing Street characterised the discussions as "constructive", Johnson moaned that some of the leaders did not consider the UK to be one country. "I just need to get that into their heads," he said.

The PM warned that unless there was a solution he would invoke Article 16 of the protocol which allows either side to take unilateral action if its implementation were to lead to "serious economic, societal or environmental difficulties".

His comments followed a series of talks with French President Emmanuel Macron, German Chancellor Angela Merkel, European Commission president Ursula von der Leyen and European Council leader Charles Michel.

The Prime Minister told Sky News: "I think we can sort it out but ... it is up to our EU friends and partners to understand that we will do whatever it takes.

"I think if the protocol continues to be applied in this way, then we will obviously not hesitate to invoke Article 16, as I have said before.

"Don't forget, the EU themselves invoked Article 16 in January, to disapply the protocol, so they can stop removal of vaccines from the EU to the UK.

"I've talked to some of our friends here today, who do seem to misunderstand that the UK is a single country, a single territory. I just need to get that into their heads."

The protocol – which is intended to protect the peace process – effectively keeps Northern Ireland in the European single market to avoid a hard border with the Republic, meaning a trade barrier in the Irish Sea for goods crossing from Great Britain.

Macron and von der Leyen have both insisted that the protocol is the only way to ensure an open border on the island of Ireland and that there can be no renegotiation of its terms.

The National: Emmanuel Macron with Boris Johnson at the G7 summit in Cornwall Emmanuel Macron with Boris Johnson at the G7 summit in Cornwall

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However, the UK has complained the EU's "purist" interpretation of the rules is strangling trade between Britain and Northern Ireland and leading to a rise in sectarian tensions – particularly among Unionists who fear their place UK is under threat.

Downing Street has previously indicated the Government would be prepared to unilaterally delay the full implementation of the protocol to prevent a ban on chilled meats crossing the Irish Sea from Britain.

Restrictions on British-produced chilled meats entering Northern Ireland are due to come into force at the end of the month.

Delaying the checks without Brussels' agreement risks triggering a "sausage war" trade dispute, with the EU threatening to respond to any breach of the deal signed by the Prime Minister.

Johnson insisted that he did not want to see a trade war, but said that it was up to the EU whether the protocol was applied "in a pragmatic way or a theologically draconian way".

"I think the treaty we signed – I signed – is perfectly reasonable. I don't think that the interpretation or application of the protocol is sensible or pragmatic," he said.

"What I'm hearing from our friends in the EU is that they understand the strength of our feelings on this, and they understand why governments might want to protect the territorial integrity of the UK, plus the UK's internal market.

"I think that the protocol can work if it is sensibly applied but at the moment there is - it's not just a question of chilled meats or sausages, there are all kinds of impediments being constructed, and we need to sort it out."

Meanwhile, the main business of the summit will see the leaders discuss building resilience to future crises, consider foreign policy and then decide on their response to Covid-19.

The group will commit to a new plan – the Carbis Bay Declaration – to quash future pandemics within the first 100 days, while the UK is creating a new animal vaccine centre aimed at preventing future diseases crossing to humans.

As part of Johnson's "Global Britain" agenda, the leaders of South Korea, India, Australia and South Africa will also take part in summit events, expanding the G7 to take in other prominent democracies.

Those leaders attending the event – India's Narendra Modi is participating remotely because of the coronavirus crisis in his country – with a beach barbeque toasting marshmallows around fire pits.