European Commission First Vice-President Frans Timmermans delivers a speech during a debate on the situation in Hungary at the European Parliament in Strasbourg, France, September 11, 2018. REUTERS/Vincent Kessler

BRUSSELS (Reuters) - Britain cannot leave the European house but keep the key and the right to swing by anytime, a top European Union official told London as Brexit negotiations are entering their final stretch.

Speaking at the European Parliament’s plenary session in Strasbourg, deputy head of the EU’s executive, Frans Timmermans said: “We are all under the obligation to do as little harm as possible. That is in the interest of all Europeans, whether they are in the United Kingdom or on continent.”

“But let me be clear... if somebody says ‘I want to leave your house, but I’ll take the key and I will come back whenever I like and take whatever I like from that house.”, that doesn’t work,” Timmermans told the sitting.

Timmermans said the issue of avoiding border infrastructure and checks between EU member state Ireland and Britain’s province of Northern Ireland was “central to our responsibility to do as little harm as possible in these negotiations.”

Britain is due to become next March the first country to ever leave the EU - but the two have yet to agree on divorce terms or future rules on cooperating on everything from security and trade to air traffic.