Britain’s role at the heart of Europe is crucial in combating terrorism and illegal mass migration, the head of Nato has said on the eve of the UK referendum on EU membership.

In an interview with the Guardian at Nato headquarters in Brussels, Jens Stoltenberg, the secretary general, also said a fragmented Europe would exacerbate instability in the region.

“I don’t have a vote. It’s up to the people of Britain to decide,” Stoltenberg said. “What I can do is tell you what matters for Nato, and a strong UK in a strong Europe is good for the UK and it’s good for Nato, because we are faced with unprecedented security challenges, with terrorism, with instability and an unpredictable security environment, and a fragmented Europe will add to instability and unpredictability.”

His intervention came on the last day of campaigning before Thursday’s vote. Senior politicians on both sides of the close-fought referendum battle are crisscrossing Britain in the final hours, with the result still too close to call.

Stoltenberg was just one of a number of European statesmen to weigh in on the eve of the referendum.

France’s president, François Hollande, said the European Union’s future was at stake on Thursday. “There’s a very serious risk for the United Kingdom not to be able to access the common market and … the European economic area any more,” he said. France would “draw all the conclusions” of a vote to leave. “This would be irreversible.”

Belgium’s prime minister, Charles Michel, said that whatever the outcome of Thursday’s vote, he would seek a special meeting of European Union leaders to assess what had sent the bloc off the rails. Michel said he wanted an informal meeting because “there is this clear signal all over Europe, not only in Britain” of discontent. “We feel more and more hesitation about the European project,” he told the VRT network.

The head of the European commission, Jean-Claude Juncker, warned British voters there would be no reopening of talks on Britain’s place in the EU in the event of a vote to leave. “Out means out,” he said. “British policymakers and British voters have to know that there will be no kind of renegotiation.

“We have concluded a deal with the prime minister. He got the maximum he could receive and we gave the maximum we could give. So there will be no renegotiation,” Juncker said.



Many Nato officials are concerned that what they see as the two biggest threats to European security – Islamic State, together with other Islamic extremists, and a newly aggressive Kremlin – both have the fragmentation of Europe as a strategic goal.

“The UK is the biggest force provider among European Nato allies, so it matters what the UK does and for Nato it is an advantage to have UK leadership inside the European Union being a strong advocate for transatlantic cooperation and also for EU-Nato cooperation,” Stoltenberg said.

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Stoltenberg, who has been Nato secretary general since 2014, said Britain acted as an important bridge between the EU and Nato and promoted the sharing of information on the terrorist threat. EU-Nato cooperation had been instrumental in curbing the mass movement of people across the Aegean Sea, he added.

“To fight the terrorist threat we need both the EU and Nato and we need stronger cooperation between Nato and the European Union,” he said. “And the UK is pushing and showing leadership in pursuing that both from inside Nato and from inside EU. If our neighbourhoods are more stable, we are more secure.”

Stoltenberg, a former prime minister of Norway, pointed out that his country had opted not to join the EU in a 1994 referendum, and now had a much higher rate of immigration for its size than the UK.

He said cooperation between the EU and Nato on cyber-defences and on blocking people trafficking was increasing.

“The UK is a kind of bridge between the EU and Nato and also a bridge between Europe and the United States. And this is important for UK, the US and for Nato,” he said. “No one of us has all the tools in the toolkit, so we have to work together and the UK is a key ally in facilitating that.”

Stoltenberg campaigned for his country to join the EU in 1994, and he said that while he respected the voters’ decision to stay out, he had not changed his mind on the advantages of EU membership.

“The arrangement [Norway] now has with the European Union is that we pay a huge amount of money to the European Union. We implement EU decisions and directives, but we don’t have a say. We are not at the table,” he said.

“Norway actually receives more migrants compared to its size than the United Kingdom … significantly more, compared to the size. So even if you stay outside the European Union you are affected by decisions made inside Europe, and so I think it’s better to be at the table influencing those decisions and those developments instead of being outside but being affected by decisions by the European Union.”

On the prospect of a European army, in the shape of greater European military integration with a European command headquarters, Stoltenberg said any move towards more European resources being put into defence was to be welcomed, while duplication of structures was not.

He said it was not clear how ambitious the EU foreign service’s plans for common defence would be, but added that the UK was an important voice inside the EU helping to prevent any such duplication between the EU and Nato.



Another Nato official said: “The UK voice has been critical in stopping the EU trying to fill roles that are already performed by Nato. What we are concerned about is if we lose that voice on the inside in Brussels.”