EU Commission president Ursula von der Leyen on Wednesday (18 December) said it will be "extremely challenging" to negotiate a trade deal with the UK in 11 months next year.

The new commission chief warned the UK that if there is a real cliff-edge at the end of next year, it will hurt Britain more than the EU.

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Britain is set to leave the bloc on 31 January. If the Westminster and the EU parliaments ratify the withdrawal agreement by then, a transition period will kick in- but it only lasts until the end of the year.

During the transition period Britain will remain in the EU's customs union and single market, until 31 December 2020 - and then newly-negotiated arrangements will have to apply on trade, fisheries and security.

Von der Leyen said the EU commission will propose a comprehensive negotiating mandate on 1 February.

But the commission would want to deal with the most pressing issues first, where there could be no unilateral or contingency measures to replace existing arrangements.

"The timetable ahead of us is extremely challenging. […] It leaves us very little time," she told MEPs in Strasbourg. "In case we cannot conclude an agreement by the end of 2020, we will face again a cliff-edge situation," the former German defence minister added.

But she said while a cliff-edge situation would harm EU interests, it will have a more profound impact on the UK, "as the EU will continue benefitting from its single market, its customs union and the more than 700 international agreements".

Von der Leyen's warning comes as British prime minister Boris Johnson, who last week won a comfortable majority in the UK general election, plans to pre-emptively block any attempt to extend the transition period.

Britain has until 1 July 2020 to ask the EU for an extension to the transition period.

Johnson is planning to present his Brexit legislation to parliament on Friday, with a legal block on any extension. MPs are expected to vote in January.

Barnier's back

On Tuesday, EU chief negotiator Michel Barnier also warned that the negotiations have to be phased.

"It may not be possible in this limited time to do everything, but we will do everything possible," the EU chief negotiator Barnier said in his comments to MEPs.

Barnier said other, less pressing matters can be negotiated with the UK at a later stage.

The first stage of talks will have to focus on duty-free zero-tariff trading in goods, a regulatory level playing field which is crucial for the EU so that the UK does not undercut it on environmental and workplace standards, and access to fishing waters.

"The idea of a level playing field will be our guide in the next stage of negotiations, EU council president Charles Michel said in the parliament. The UK will likely have to sign up to EU rules on state aid, tax and the environment.

The EU will treat these issues as a package, and will again move the negotiations in sequences, a concept which has worked in favour of the EU during the divorce talks.

EU-27 Brexit diplomats will meet intensively in January to help prepare the commission's negotiating mandate.