European Commission President Ursula von der Leyen | Sean Gallup/Getty Images Von der Leyen to departing Brits: Things will change ‘There’s a great difference between being a member country or not,’ says European Commission president.

Britain’s departure from the European Union will make it harder for the country to profit from the bloc’s lucrative market, European Commission President Ursula von der Leyen said.

“One thing has to be clear: There’s a great difference between being a member country or not,” von der Leyen told German television Friday evening, hours before the United Kingdom left the bloc.

“Access to the European Single Market — the largest single market in the world — will become more difficult for our British friends,” she said.

Britain left the EU Friday night after 47 years of membership, after British voters approved the departure in a referendum over three-and-a-half years ago.

The bloc of remaining 27 EU countries and the U.K. have agreed that for a transition period until the end of the year, current rules and regulations will remain in effect, giving them 11 months to negotiate the details of their future relationship on issues ranging from trade to product standards to cross-border data flows.

"We will work day and night [and] we are in a strong starting position. At the end of the year, we will see where we stand," von der Leyen said Friday, adding that "we will only put a signature under a treaty once everything has been negotiated and once we have come up with a balanced package."

She said the negotiations so far had shown “the high value of unity” for the EU. It has paid off for the EU27 to “stand together, be united and conduct the negotiations calmly and fairly,” she said.