Britain should stay in the EU to ensure it has a "seat at the bargaining table" in the future, Germany's Chancellor Angela Merkel has said.
Asked about her view on the impending membership referendum in the UK, Ms Merkel revealed she "personally" hoped Brits would vote to remain come June 23.
Cooperation between member nations and the UK over the single market "has always been very good", she said, as she urged the country to help it develop for the "digital age".
You will never get a really good result in negotiations, particularly on very important issues, when you're not in the room and giving input.
She warned that Britain would not get the same "quality of compromise" if it was outside the EU, and sharing the costs of the single market as well as its benefits.
"No one individual country on its own is able to bring about good results. It would be not only be in our interests, but also in the interests of Britain, when it can bring its whole political weight to the negotiating table as part and parcel of the European Union," she added.
Leave campaigner Boris Johnson said the interventions from EU leaders showed they had "hit the panic button" but Remain campaigners defended the statements.
Former foreign secretary and Remain supporter, Sir Malcolm Rifkind, told ITV News it would be "pretty dumb" for Britain to expect to influence the EU from outside of the bloc.
He said it was right for world leaders like Mrs Merkel and US President Barack Obama to enter a debate within other nations.
(Imagine) if it was the other way round, if people were asking us now who do you think should be the next president of the United States, Donald Trump or Hillary Clinton? The idea that we would say "nothing to do with us, we can't have a view, we can't have an opinion, we must be Trappist monks," would be very silly.