UPDATE 1-EU's Tusk says "backstop" part of Brexit deal not renegotiable

European Council President Donald Tusk said the EU-UK divorce deal was not up for renegotiation after Britain's parliament on Tuesday voted to replace the Irish "backstop" border arrangement contained in it with unspecified "alternative arrangements".

The backstop is aimed at keeping an open border between EU member Ireland and British-ruled Northern Ireland after Brexit but is strongly opposed by many in Prime Minister Theresa May's Conservative Party, who say it risks trapping the UK in a permanent customs union with the European Union. "The Withdrawal agreement is and remains the best and only way to ensure an orderly withdrawal of the United Kingdom from the European Union," Tusk said via a spokesman.

"The backstop is part of the Withdrawal Agreement, and the Withdrawal Agreement is not open for renegotiation." The House of Commons also backed on Tuesday a non-binding amendment to rule out a damaging no-deal Brexit, a move welcomed by Tusk.

"We welcome and share the UK parliament's ambition to avoid a no-deal scenario. We continue to urge the UK Government to clarify its intentions with respect to its next steps as soon as possible," Tusk said, in comments agreed with the 27 EU states remaining in the bloc after Brexit. "If the UK's intentions for the future partnership were to evolve, the EU would be prepared to reconsider its offer and adjust the content and the level of ambition of the political declaration... Should there be a UK reasoned request for an extension, the EU27 would stand ready to consider it and decide by unanimity."

Tusk added that the EU would press on with contingency preparations as well as the ratification of the existing Withdrawal Agreement that has stalled on the UK side. (Reporting by Gabriela Baczynska; Editing by Gareth Jones)