Brussels — Any long Brexit delay would pile on economic and political costs for the European Union, the bloc’s chief negotiator Michel Barnier said on Tuesday, stressing that these would need to be weighed up carefully against potential benefits. Barnier spoke ahead of an EU leaders’ summit on Thursday and Friday where they could decide on postponing Brexit beyond the current date of March 29, should British Prime Minister Theresa May request that. “It is our duty to ask whether this extension would be useful. It would extend uncertainty and uncertainty costs. We cannot prolong uncertainty without having a good reason for it,” Barnier told a news conference 10 days before Brexit is due to happen. “EU leaders will need a concrete plan from the UK in order to be able to make an informed decision,” Barnier said. He said the other 27 national leaders would ask May whether delaying Brexit would increase the chances that her fractious parliament would ratify their stalled Brexit deal. Bar...

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