In a major blow to Prime Minister Theresa May and her Brexit team, Britain's three-judge High Court has ruled that Article 50 can be triggered only by an Act of Parliament, and not by the government alone.

The historic ruling, delivered yesterday by Lord Chief Justice John Thomas, is likely to significantly delay Britain's exit from the European Union as MPs debate and table motions in order to have a say in Mrs May's negotiation strategy and soften her "hard Brexit" stance.

What seems unlikely is a U-turn on the decision to leave the EU, as MPs will not blatantly defy the will of the majority of British voters. In the June 23 referendum, 52 per cent of Britons voted for an exit from the EU, which it joined on Jan 1, 1973.

Yesterday, the Lord Chief Justice said: "The most fundamental rule of the UK's Constitution is that Parliament is sovereign and can make and unmake any law it chooses."

Mrs May's government said in a statement it was disappointed by the court's ruling. "The country voted to leave the European Union in a referendum approved by an Act of Parliament. And the government is determined to respect the result of the referendum," it said.

Downing Street later said it still intends to invoke Article 50 before the end of March, as Mrs May had promised. It also said it is lawful for the government to use its prerogative powers to start the Brexit process. A spokesman said the government will appeal to the supreme court against the ruling. The hearing will take place next month.

Sterling rose on news of the judgment, as investors felt optimistic that lawmakers would scrutinise Mrs May's policies and ensure that she has an economically favourable Brexit blueprint.

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