More than 1,000 barristers and advocates have urged the prime minister to allow Parliament to determine whether the UK should leave the European Union or not following the referendum in favour of Brexit.

Signatories to a letter sent to David Cameron have argued there must be a free vote in Parliament before Article 50 TEU is triggered, commencing the withdrawal process.

It states: “The referendum did not set a threshold necessary to leave the EU, commonly adopted in polls of national importance, eg, 60% of those voting or 40% of the electorate. This is presumably because the result was only advisory.

“The outcome of the exit process will affect a generation of people who were not old enough to vote in the referendum. The positions of Scotland, Northern Ireland and Gibraltar require special consideration, since their populations did not vote to leave the EU.

“The parliamentary vote should take place with a greater understanding as to the economic consequences of Brexit, as businesses and investors in the UK start to react to the outcome of the referendum.

“For all of these reasons, it is proposed that the government establishes, as a matter of urgency, a royal commission or an equivalent independent body to receive evidence and report, within a short, fixed timescale, on the benefits, costs and risks of triggering article 50 to the UK as a whole, and to all of its constituent populations. The parliamentary vote should not take place until the commission has reported.”

Constitutional expert Aidan O’Neill QC, of Matrix Chambers, said: “The Brexit referendum has made clear that the UK is not a united nation state, but a divided state of nations. It has given no mandate or guidance as to what our nations’ future relationship might be with Europe, and with each other.

“If the UK is to survive the result of this vote, a consensus needs to be built up about the way forward. Fully informed discussions and deliberations within and between our parliaments is the only proper constitutional way to achieve this. Precipitate or unilateral action by the UK government to trigger article 50 will simply further divide us.”

Philip Kolvin QC, who co-ordinated the initiative, added: “Parliament is sovereign and the guardian of our democracy. MPs are elected to exercise their best judgment on the basis of objective evidence, to safeguard the interests of the country and their constituents for this and future generations. At this time of profound constitutional, political and possibly social and economic crisis, we look to them to fulfil the responsibility placed upon them.”