Fail migration test and UK could quit, Tusk warns EU

By Alastair Macdonald BRUSSELS (Reuters) - European Council President Donald Tusk warned European Union leaders on Wednesday that if they fail to end disputes over how to handle the migration crisis they could help drive Britain out, undermining the bloc. Addressing a debate in the European Parliament on issues discussed by the summit he chaired last week, Tusk said how the EU handles migration would be "of key significance" to the outcome of June's British referendum on whether to leave the EU. "All those who want to keep the unity of the European Union, the unity of the whole of the West ... should back such a common plan with the fullest determination possible," the former Polish premier said of EU plans for a common policy on migration. "If this emerging unity of action on the migration crisis is violated -- by anyone -- they may in fact contribute to the UK leaving the EU." He spoke shortly after Hungarian Prime Minister Viktor Orban, an outspoken critic of the EU's efforts to take in refugees, promised a referendum on EU plans to redistribute asylum seekers to all 28 states according to mandatory quotas. Speaking to Reuters after the debate, Tusk said he was still seeking to ascertain exactly what Orban was proposing and so had no comment on the Hungarian referendum suggestion. Orban set no timeframe for the vote and EU officials said he may be more concerned to block plans for a future permanent relocation scheme than to try to undo the short-term one agreed last year. In his comments to parliament, Tusk made no reference to specific governments. All 28 EU interior ministers will meet again in Brussels on Thursday to discuss the crisis ahead of a summit on March 7 with Turkey, whose help the Europeans have sought in stemming the flow of people heading for Greece. EU officials are concerned that what they see as populist and nationalist measures and statements could undo what Brussels sees as a fragile consensus emerging on how to bring together a number of measures to counter a year of chaos. Earlier in the debate, Tusk weighed into a controversy in Britain over whether the EU reform deal he brokered and which leaders agreed with British Prime Minister David Cameron on Friday could be overturned by the EU's judicial processes. Tusk said it was "legally binding and irreversible", "in conformity with the treaties and cannot be annulled by the European Court of Justice". (Reporting by Alastair Macdonald; Editing by Catherine Evans)