The German president has made a direct appeal to the British public not to vote in favour of the UK leaving the European Union.
In a televised address delivered on Friday, Joachim Gauck said he had "listened with interest" to David Cameron's speech in which he pledged to renegotiate Britain's membership of the EU and then put it to a public ballot in 2017.
"Of course, it is up to the British to decide on their own future, but perhaps they are prepared to listen to an appeal from Schloss Bellevue," Gauck said. Schloss Bellevue is the official residence of the president, who has a largely ceremonial role.
In a nationally televised address, he said: "Dear people of England, Scotland, Wales and Northern Ireland, dear new British citizens! We would like you to stay with us! We need your experience as the oldest parliamentary democracy, we need your traditions, your pragmatism and your courage!
"During the Second World War, your efforts helped to save our Europe – and it is also your Europe. Let us continue to engage in discussion on how to move towards the European res publica, for we will only be able to master future challenges if we work together. More Europe cannot mean a Europe without you!"
Cameron forged an alliance with German chancellor Angela Merkel at the recent EU budget negotiations, enabling him to return to London victorious in his attempts to cut Brussels' funding.
However the move did not meet with universal acclaim in Berlin. On Thursday, the leader of the Social-Democratic opposition, Peer Steinbrueck, attacked Merkel for making a "strange alliance" with Cameron.
"We need partners who see their future in Europe and do not rely on those who want to leave," he said.
It is not just other European nations that are concerned the UK may opt to exit the union. The United States has been increasingly vocal in its calls for Britain to remain at the heart of Europe.
On Thursday the US ambassador to the EU, William E. Kennard told the Huffington Post UK that "the US supports a strong UK in a strong EU".
The message is likely to be repeated by the new secretary of state John Kerry when he arrives in London to meet William Hague next week.