European Commission President Ursula von der Leyen speaks during a news conference at Government Buildings in Dublin, Ireland January 15, 2020. REUTERS/Lorraine O'Sullivan

DUBLIN (Reuters) - It will ultimately be up to Britain whether or not it seeks more time to negotiate a trade agreement with the European Union after it leaves the bloc, the head of the European Commission said on Wednesday.

Britain is set to leave the EU on Jan. 31 after agreeing a divorce deal late last year but will remain bound by all the bloc’s rules until the end of 2020 under an agreed transition phase aimed at smoothing its exit.

British Prime Minister Boris Johnson insists he will not ask for more time, even as European leaders, including EU Commission President Ursula Von der Leyen, cast doubt on the feasibility of agreeing a trade deal over the next 11 months.

“There is only one of the two who can ask for an extension and that is the United Kingdom. We will see mid-year where we are at,” Von der Leyen told a news conference in Dublin.

She said that Brussels was well-placed to move as fast as possible following her meeting with Johnson last week.

A spokesman for Von der Leyen added that while both sides can formally ask for an extension, it would have to be commonly agreed to.

If the transition period is not extended beyond 2020, trade relations between the EU and Britain from the start of 2021 will either be governed by whatever agreement can be hammered out by the end of this year, or by World Trade Organization rules.

Johnson has also insisted there will be no customs checks between Northern Ireland and the rest of the UK after Brexit.

But Von der Leyen said border controls between the two are clearly laid out in the divorce agreement Britain signed up to.