LONDON (Reuters) - A group opposed to Britain’s exit from the European Union has accused the government of refusing to allow it to make public the official justification for triggering Article 50 to start the Brexit process without a parliamentary vote.

Pro-Europe demonstrators protest during a "March for Europe" against the Brexit vote result earlier in the year, in London, Britain, September 3, 2016. REUTERS/Luke MacGregor

The British government’s position is that it has no legal obligation to consult parliament on invoking Article 50 of the EU’s Lisbon Treaty which will give Britain a two-year period to work out the terms of its departure.

The People’s Challenge, which is financed by a crowdfunding campaign, said it had planned to make public the government’s written legal defence of its position on triggering Article 50 alongside its own lawyers’ submissions to court so that the country could see and engage with the competing arguments.

But it said the government was insisting that every word of its defence must be kept confidential.

The People’s Challenge on Friday lodged an urgent application to the court to allow it to publish the government’s argument. The court is yet to rule on this application.

“The Prime Minister’s reasons for believing that she alone is empowered to take Britain out of the EU cannot be treated as a state secret and the extraordinary stakes in this case mean that justice must be as open as possible,” John Halford, solicitor for The People’s Challenge, said.

A government spokesman said the non-disclosure was not a decision taken by the government but by the court.

“The court has considered it appropriate to put in place a confidentiality order for reasons including the threats received by some claimants. It is important that this court order is adhered to,” he said.

The People’s Challenge has also filed evidence and detailed legal submissions as to why it would be unlawful for the government to invoke Article 50 without parliament’s authority and full involvement through the legislative process.

Prime Minister Theresa May has made clear she will not give a running commentary on Brexit or lay out all her negotiating cards in public, though some aides have suggested her plan is to invoke Article 50 early in 2017.