Hundreds of barristers have written to Prime Minister David Cameron saying the referendum result is "advisory", and not legally binding.
More than 1,000 lawyers have signed the letter, which asks Mr Cameron to tread carefully before taking steps to withdraw the UK from the European Union.
They say primary legislation is needed before Article 50 - the route member states can leave the EU - can be triggered, and are calling for the Government to organise an independent investigation into the pros and cons of withdrawal before making exit plans.
The letter, which they say should arrive later this week, proposes a way forward that "reconciles the legal, constitutional and political issues" triggered by the Brexit result.
One barrister involved, Aidan O'Neill, an EU law specialist, said: "The Brexit referendum has made clear that the UK is not a united nation-state, but a divided state of nations.
"But it has given no mandate or guidance as to what our nations' future relationship might be with Europe, and with each other.
"[Triggering] Article 50 will simply further divide us", he added.