David Cameron is reported to have asked Angela Merkel not to wade in to the UK's referendum debate

Editor’s Note: Nicolai von Ondarza is deputy head of the Europe research division at the German Institute for International and Security Affairs (SWP) in Berlin. He specializes in issues of EU governance and British EU policy. The opinions expressed here are his own.

Berlin CNN  — 

U.S. President Barack Obama appealed directly to the British people to vote to remain; the IMF and the OECD warned of the grave economic consequences of “Brexit;” even China’s President Xi Jinping expressed his hope that the UK would stay in the European Union.

But – with just weeks to go before Britain votes in a referendum on its future – the leaders of EU countries and institutions have remained stubbornly silent on a decision that will shape the future of the whole Union.

This nervous silence is particularly noticeable in Berlin, one of the UK’s closest allies in Europe.

Chancellor Angela Merkel, regarded by many Britons as Europe’s most powerful politician, held her last speech on the UK’s role in Europe back in 2014, when the In-Out referendum was still only an option in the distant future.

Even after the compromise on the “new settlement of the United Kingdom in the European Union” in February 2016, the German government made no comment on the referendum, other than a short expression of hope that the UK would remain in the EU.

At the same time, the shadow of a possible “Brexit” looms large over practically every debate on foreign and EU politics in Berlin these days.

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‘Do no harm’

The perils of external involvement in referenda on EU issues is a lesson European political elites have learned the hard way in recent decades.

Since 1972, a total of 54 referenda have taken place on issues of European integration. Most were called by national governments to legitimize EU accession or treaty reform, but in recent years there has been an increase in the use of referenda as a tool against the EU, such as the Dutch referendum to reject the EU-Ukraine Association Agreement in April.

And in all of these referendums one lesson stood out: External involvement from other EU partners always carries a risk of backfiring.

Most clearly, warnings by EU Commission President Juncker during the Greek referendum on its economic reform program in the summer of 2015 were perceived as threats by the Greek public and led to a hardening of its stance against austerity reforms.

As a result, British Prime Minister David Cameron himself is said to have asked Chancellor Merkel and others to keep quiet during the EU referendum campaign, according to Germany’s Der Spiegel news magazine.

This has resulted in a “Do no harm” strategy employed by Brussels and Berlin:

First and foremost, EU politicians must refrain from any direct public interventions in the debate, let alone any campaign speeches on the island.

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Easy target

EU leaders like Juncker, other EU commissioners or European Parliament president Martin Schulz are regarded as toxic by the UK’s right-wing press and politicians, and would only provide welcome targets for the Leave campaign.

Juncker explained in a recent interview that he will not campaign in the UK “because the European Commission is even more disliked in Britain than Germany.”

The one possible exception may be British EU commissioner Jonathan Hill, although his few statements on Brexit have hardly reached a widespread audience in the UK.

German politicians face a special predicament; although the image of Germany has improved noticeably in the UK in recent years, any kind of direct intervention that could be perceived as a threat by German politicians would be seen as hostile, and inevitably backfire.

References to World War II and the threat of German domination are still easily evoked in British public discourse.

Iain Duncan Smith, Secretary of State and Pensions until March 2016 and a prominent supporter of the Leave campaign, claimed that Merkel was silently present in the minds of the UK cabinet during the whole renegotiation process, helping to steer Cameron’s hand. The strongly Eurosceptic Sun newspaper (among others) immediately picked this comment up, proclaiming on its front page that “Cameron surrendered to Merkel.”

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Wall of silence

So far, there has been only one exception to this strategy of non-involvement.

When Boris Johnson, the former Mayor of London and most prominent supporter of the Vote Leave campaign, compared the EU’s ambition to unify the countries of Europe to those of Mussolini and Hitler, he hit a nerve in Brussels.

In the EU’s most direct intervention so far, European Council President Donald Tusk said in this case he “could not remain silent” and that Johnson’s Hitler comparison amounted to “political amnesia.”

But other than that, the EU institutions have kept up their wall of silence.

In the upcoming heated debates before the UK referendum, European politicians’ and bureaucrats’ resolve to keep up the policy of not commenting on Brexit will surely be severely tested.

On May 27, the so-called “purdah period” officially began, during which the UK government is prohibited from officially intervening in the EU debate. This leaves the job of defending the UK’s EU membership mainly in the unlikely hands of Cameron.

It’s a risky strategy, since if Britain becomes the first member state to leave the EU, Juncker and Merkel will share the blame.

But if EU leaders do not want to negatively impact the referendum, they must stick to their guns: It is Cameron’s referendum, and the battle is his to fight.

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Nicolai von Ondarza is deputy head of the Europe research division at the German Institute for International and Security Affairs (SWP) in Berlin. He specializes in issues of EU governance and British EU policy. The opinions expressed here are his own.