The result of June's vote was not legally binding...
A lawsuit brought by a group Bloomberg describes as "a hairdresser, a finance entrepreneur and others unwilling to be publicly identified" is turning into a controversial case which could test the limitations of the power of the office of Prime Minister in the UK.
The plaintiffs argue that Article 50 should not be triggered by the PM without a vote taking place in parliament.
If the case is successful it would create a legal mechanism for the House of Commons to overrule the result of the referendum.
This graph from Morgan Stanly reflects the Brexit divide between MPs and suggests that a vote on the article could have enough support to overrule the referendum result.
Jeff King, a professor at University College London told the financial news service that this "will be one of the most important constitutional law cases ever decided."
If the vote happened and the public's desires were overruled, the 'Leave' campaign would be likely to take a case to the European Court of Justice.