The EU's chief Brexit negotiator Michel Barnier said Tuesday that the bloc was prepared for a no-deal Brexit scenario.
Barnier acknowledged that the UK's House of Commons had voted against leaving the EU without a deal last week but cautioned: "Voting against a No Deal does not prevent it from happening."
His advice then followed: "Finalise all preparations for a no-deal scenario."
The negotiator said that the European Parliament and European Council had now approved nearly all foreseen contingency measures but were still working on the issues of short-term visas and the EU budget for 2019.
Extension to Article 50
If British Prime Minister Theresa May requests an extension to the Article 50 period before the Spring European Council on Thursday, the 27 leaders would assess the "reason" and "usefulness" of this solicitation, said Barnier.
British MPs voted last Thursday to push back the UK's departure from the EU until at least June 30, 2019, if parliament agrees to a withdrawal deal by March 20.
On Tuesday, May's spokesperson said she would write to European Council President Donald Tusk to request a delay to Brexit either the same day or on Wednesday.
"EU leaders will need a concrete plan from the UK in order to be able to make an informed decision," Barnier added.
The bloc will want to determine if an extension increases the chances of the Withdrawl Agreement being ratified or if the UK is asking because it wants more time to rework the political declaration.
"How can we ensure that at the end of a possible extension that we are not back in the same situation as today," the EU official said.
The bloc, he added, would assess what was in its best interests, as "extending the uncertainty without a clear plan" would incur further costs for its businesses and a possible political cost for the EU.
"It is for the British government and parliament to decide very quickly what the UK wants to do next," Barnier concluded.
The British government was on Tuesday considering its next moves on Brexit after the parliament speaker derailed its plans for a third vote on the EU withdrawal deal.
House of Commons Speaker John Bercow said May's Brexit deal could not be voted on again unless a different proposal was submitted. The deal has already been heavily defeated twice.