British politicians sowed the seeds for Brexit by blaming the European Union for problems over which the bloc has little control and while building an economy dependent on foreign labour, the president of the European commission has said.

Writing exclusively for the Guardian as EU leaders meet to celebrate the bloc’s 60th anniversary in Rome, Jean-Claude Juncker warns that “for too long” politicians at a national level have allowed the EU to be a scapegoat, and that the consequences can now be seen.

As well as making an impassioned call for members of the “new Europe of 27” to reaffirm their commitment to the union, and take ownership of its future, Juncker turns his fire on those who laid down the foundations for Britain’s decision on 23 June to leave the EU.

In remarks that will be regarded by some as contentious, he points out that on the most salient issues of the referendum campaign, the EU is largely powerless to intervene, including on limiting immigration to the UK.

“We should not pretend that Europe alone can solve all problems,” Juncker writes. “‘Brussels’ should not have been constantly blamed in British political discourse for things for which the EU is not responsible: we now know the result of such rhetoric.

“For example, the EU has few powers in three of the four areas of policy that are usually most controversial in UK elections: healthcare, education and welfare.

“On the fourth, immigration, free movement is integral to the EU’s single market, which the UK has always strongly supported, and is a right with clear limits. Furthermore, most immigration to the UK comes from outside the EU, where policy is made by the UK alone.

“It is also the UK that decides on the structural economic issues that have led to high demand from British employers for migrant labour.”

According to the latest data from the Office for National Statistics, inward migration to the UK was estimated to be 596,000 in the year ending September 2016, comprising 268,000 EU citizens, 257,000 non-EU citizens and 71,000 British citizens.

In the last two years, the number of immigrants from the EU only marginally eclipsed the numbers coming from further afield, following a long period when the numbers coming from non-EU states was far higher.

Speaking separately to the Financial Times, Juncker described David Cameron as a “destroyer”. He said: “I have met in my life two big destroyers: Gorbachev, who destroyed the Soviet Union, and Cameron, who destroyed the United Kingdom to some extent, even if there is no wave of Scotland to become independent.”

The european commission president also said he told US vice-president Mike Pence of the dangers in Donald Trump encouraging member states to follow the UK. “I told him: ‘Do not invite others to leave, because if the EU collapses, you will have another war in the western Balkans,” he said.

Leaders of the 27 remaining EU member states are gathering in Rome in a show of unity less than a week before the UK intends to formally begin its exit from the bloc. Theresa May, who plans to trigger article 50 on 29 March, was not invited to Rome.

Italian police say they expect around 25,000 people to attend both pro- and anti-EU rallies during the summit, with the security services on high alert just days after the London attack.

The EU heads of state or government will have an audience with Pope Francis at the Vatican on Friday evening. On Saturday, they will assemble in Rome’s Orazi and Curiazi Hall of the Capitol, in the Piazza del Campidoglio, to affirm their support for the EU. It is the same venue where the 1957 treaties were signed.

The leaders are expected to offer their support for a “Rome declaration” which will pay testament to the achievements of the EU in maintaining peace over six decades, while warning that the union is now facing “unprecedented challenges, both global and domestic: regional conflicts, terrorism, growing migratory pressures, protectionism and social and economic inequalities”.

In his article for the Guardian, Juncker writes: “As we mark the 60th anniversary of that fateful date, we are also marking the birth of the European project anew.”

He says there are problems for which only collective solutions can be effective, and that he is looking forward to negotiating a new relationship with the British government once the terms of departure have been agreed.

Asked in a BBC interview broadcast on Friday morning about the accuracy of reports that the UK would be asked to pay £50bn to leave the EU, a potential hurdle to progress in negotiations, Juncker responded: “It’s around that but that’s not the main story. We have to calculate scientifically what the British commitments were and then the bill has to be paid.”

In his article for the Guardian, Juncker adds: “Pollution, terrorism and organised crime, to give just three examples, do not stop at national borders. So without collective policymaking there can be no effective policy on those matters.

“We need firm action within the EU, rooted where necessary in EU law. We also need close cooperation with external partners … that includes partnership with the UK once we have negotiated the terms of its departure.”

The Rome declaration’s initial draft, which supported a proposal from the German chancellor for formalising a “multi-speed Europe”, was watered down following opposition from east European states.

The Polish government, which bears a grudge against its compatriot, the European council president, Donald Tusk, had threatened to refuse to support the declaration, although EU officials said they were confident that much of the rhetoric was for show.

The declaration now avows: “We will act together, at different paces and intensity where necessary, while moving in the same direction, as we have done in the past, in line with the treaties and keeping the door open to those who want to join later. Our union is undivided and indivisible.”

Meanwhile, Tusk has said that Brexit must be a one-off event and must not lead to the disintegration of the EU.

The comments were made in a 42-minute promotional film to celebrate the history of the European council, which will be given to each of the EU leaders as a gift on Saturday.

Tusk said: “The EU doesn’t have any divorce experience. We were good at broadening, not at shrinking.

“I’m convinced, however, that we will turn the corner. But the real threat today – and I think it is not only my opinion – is the disintegration of Europe in the political and ideological sense.

“It is not a coincidence that those who question liberal democracy are the same ones who call for the breakup of the EU, because the EU today is not only a political organisation which restricts national egoisms, it is also a unique territory of freedom.

“For this reason it is important that Brexit remains a one-off incident and not the beginning of a process.”