LONDON: It will be `basically impossible` to negotiate all aspects of the future relationship between the European Union and Britain by the end of this year, the head of the European Commission said on Wednesday, adding that both sides must pick priorities.

Speaking at the London School of Economics before meeting British Prime Minister Boris Johnson, Ursula von der Leyen cast doubt on his timetable for an agreement defining the long-term post-Brexit relationship by the end of 2020.

`The transition time is very, very tight ... so it is basically impossible to negotiate all that I have been mentioning, so we will have to prioritise,` she said.

Johnson has said that Britain will not extend the transition period, and will not seek a deal based on close alignment with EU rules, although his spokesman said trade talks did not need to be completed all at once.

Von der Leyen`s views are widely shared in the EU. Croatian Prime Minister Andrej Plenkovic, whose country holds the rotating six-month presidency of the bloc, told reporters that Britain had to be sensible.-Reuters