In a major setback for Prime Minister Theresa May, the UK high court has ruled that the Parliament alone has the power to trigger Brexit by notifying Brussels of the UK’s intention to leave the European Union, saia a report.

In a major ruling, the UK high court has stated that the Parliament alone has the power to trigger Brexit by notifying Brussels of the UK’s intention to leave the European Union.

The judgment, delivered by the lord chief justice, Lord Thomas of Cwmgiedd, is likely to slow the pace of Britain’s departure from the EU and is a huge setback for Theresa May, who had insisted the government alone would decide when to trigger the process, reported The Guardian.

The lord chief justice said that “the most fundamental rule of the UK constitution is that parliament is sovereign”.

In the key ruling, the lord chief justice said: "The court does not accept the argument put forward by the government. There is nothing in the 1972 European Communities Act to support it. In the judgment of the court the argument is contrary both to the language used by parliament in the 1972 act, and to the fundamental principles of the sovereignty of parliament and the absence of any entitlement on the part of the crown to change domestic law by the exercise of its prerogative powers."

Government lawyers had argued that prerogative powers were a legitimate way to give effect “to the will of the people” who voted by a clear majority to leave the European Union in the June referendum.

But the lord chief justice declared: “The government does not have power under the crown’s prerogative to give notice pursuant to article 50 for the UK to withdraw from the European Union.”

The legal dispute focused on article 50 of the treaty on European Union, which states that any member state may leave “in accordance with its own constitutional requirements” – an undefined term that has allowed both sides to pursue rival interpretations, said the report.

A government spokesman said that ministers will appeal to the supreme court against the decision. The hearing will take place early next month, it added.