Leading judges with the task of ruling on the historic Brexit legal challenge at the High Court in Britain are to give their decision today.

The announcement will be made at 10am in London by Chief Justice Lord Thomas, Master of the Rolls Terence Etherton, and Lord Justice Sales.

A number of applicants have challenged prime minister Theresa May’s strategy for Brexit in what has been described as one of the most important constitutional cases in generations.

They argue that the she has no legal power to trigger article 50 of the Lisbon Treaty to leave the EU without the prior authorisation of parliament. Ms May said at the Conservative Party conference she intends doing so by the end of March 2017.

The judges heard submissions that the British government lacks legal power to use the royal prerogative to notify article 50 and begin the process of removing statutory rights granted to UK citizens under the European Communities Act 1972, which made EU law part of UK law.

British government lawyers say that if the challenge succeeds, the government “could not give effect to the will and decision of the people, as clearly expressed in the referendum, to withdraw from the EU without further primary legislation”.

Because of the urgency and constitutional importance of the case, any appeal is expected to be heard by the Supreme Court before the end of the year.

In final submissions, Britsih government lawyers revealed any new treaty agreement with the EU following Brexit would “very likely” have to be ratified by parliament. A British Government QC said the “view at the moment” was ratification was likely if the royal prerogative was used, without prior parliamentary approval, to launch the Brexit process.

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