The European Union’s top legal adviser said the UK had the right to withdraw its Article 50 notice, and cancel Brexit plans, opening a new dimension for Prime Minister Theresa May’s plans to leave the EU, which could be rejected in Westminster next week.

The advice from the European Court of Justice’s advocate general encouraged supporters of EU membership in Britain’s parliament on the first of five days of debate on May’s plans to keep close economic ties after leaving the bloc end March.

May is confronted with a wave of criticism from the entire political spectrum, including members of her own party for the deal her government has offered to Britons. She has to enter a battle with her critics to secure parliament’s approval in the key vote on December 11 after her plan had negative response among Brexit supporters and Remainers.