The referendum was based on “misinterpretations of fact and promises that could not be delivered,” the letter says.
It argues the referendum result was merely advisory and lawmakers should have a free vote in Parliament before any British leader takes the decision to trigger Article 50 of the Lisbon Treaty – the formal EU divorce procedure.
Turnout in the June 23 referendum was 72.2 percent. A total of 17.41 million people, or 51.9 percent, voted to leave the EU, while 16.14 million, or 48.1 percent, voted to remain.
“The referendum did not set the threshold necessary to leave the EU, commonly adopted in polls of national importance, e.g. 60 percent of those voting, or 40 percent of the electorate. This is presumably because the result was only advisory,” the letter says.
“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.”
It says the parliamentary vote should take place with a greater understanding as to the “economic consequences” of Brexit, as businesses and investors in the UK react to the vote’s outcome.
The government should establish an independent body to analyze the effects of the vote, the letter further states.
“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 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.”
A prime minister acting alone under prerogative powers technically lacks the constitutional authority to invoke Article 50 without being given the authority to do so by an act of Parliament.
Westminster could refuse to ratify the vote. About two thirds of MPs are pro-EU and could block the whole process.
However, as almost 52 percent of the population voted to ‘Leave’ it is highly unlikely that Parliament would block a Brexit, as it would be seen as undemocratic.
London and Brussels appear to have reached a stalemate since the Brexit vote, as the EU has ruled out any possibility of holding informal talks on Britain’s exit before it invokes Article 50.
However, Cameron, who is stepping down in the aftermath of the vote, is resisting pressure to begin the two-year talks process as quickly as possible, insisting it is for his successor to decide when to issue the UK’s formal intention to leave the bloc.
The letter is the latest attempt by opponents of Brexit to slow or stop the divorce process.
By law, the UK’s legislatures in Wales, Scotland and Northern Ireland must be consulted before EU laws can be annulled, which could put a roadblock in EU Brexit negotiations.
Scottish First Minister Nicola Sturgeon has already said she will tell MSPs to refuse such “legislative consent” if the Scottish parliament is required to ratify the UK’s withdrawal.
At the weekend, the government turned down an online petition pleading for a second referendum, which had gained more than 4 million signatures.
A legal challenge to Cameron’s assertion that he or his successor can begin the withdrawal procedure is due to be heard in the High Court next week.