FILE PHOTO - European Council President Donald Tusk delivers a speech during a debate on the outcome of the latest European Summit on Brexit, at the European Parliament in Strasbourg, France, March 27, 2019. REUTERS/Vincent Kessler

BRUSSELS (Reuters) - The chairman of European Union leaders Donald Tusk proposed on Tuesday to offer Britain an extension of the Brexit deadline by up to one year, with the option of leaving earlier, if only Britain ratifies the existing withdrawal agreement.

In a letter to EU leaders on the eve of a summit devoted to deciding on Britain’s exit from the bloc, Tusk said that granting such a long, but flexible extension would prevent the risk of a rolling series of short extensions and emergency summits and give Britain time to rethink its strategy.

But he also said there would have to be a number of conditions attached.

“No re-opening of the Withdrawal Agreement; no start of the negotiations on the future, except for the Political Declaration; the UK would have to maintain its sincere cooperation also during this crucial period, in a manner that reflects its situation as a departing member state,” the letter said.

“We should remember, however, that the United Kingdom will remain a member state with full rights and obligations,” he said.