The European Union flag. Image: Vit Simanek/AP
A law firm has launched a legal bid to make sure that a vote in parliament takes places before the United Kingdom invokes Article 50 of the Lisbon treaty.
David Cameron has said it is up to his successor as prime minister to trigger the formal process after the UK for leaving the European Union, after voters opted to quit the bloc in last month's referendum.
But acting for a group of business people and academics, law firm Mishcon de Reya said it would be unlawful for a prime minister to do so without a full debate and vote in parliament.
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Kasra Nouroozi, a partner at the firm, said: "We must ensure that the government follows the correct process to have legal certainty and protect the UK constitution and the sovereignty of parliament in these unprecedented circumstances.
"The result of the referendum is not in doubt, but we need a process that follows UK law to enact it.
"The outcome of the referendum itself is not legally binding and for the current or future prime minister to invoke Article 50 without the approval of parliament is unlawful.
"We must make sure this is done properly for the benefit of all UK citizens. Article 50 simply cannot be invoked without a full debate and vote in parliament."
A Cabinet Office spokesperson said: "As the prime minister said in the Commons, we have now got to look at all the detailed arrangements, and parliament will clearly have a role in making sure that we find the best way forward.
"It will be important to ensure in moving ahead that the interests of all parts of the United Kingdom are protected and advanced."