The British government is quietly preparing the first draft of a bill to trigger Article 50 - the formal process to divorce the EU - in case it loses the appeal in the Supreme Court.
A senior government source said it was "sensible" for the government to draw up a bill now in order to keep Theresa May's Brexit timetable on track should it be forced to grant a vote on activating Article 50 through the UK parliament.
While in public the government has insisted its focus is on challenging the High Court ruling that it must consult the parliament on the process of triggering formal talks to leave the EU, in private ministers and civil servants are working on alternatives in the event it loses its appeal.
Sources say the government needed to begin work on a bill now in order to have enough time to push it through the prliament by a deadline for triggering Article 50 by the end of March 2017.
Primary legislation could take at least six weeks to clear both Houses of Parliament and is also subject to amendments, which gives MPs and Lords huge scope to change the tenor of the bill - making Mrs May's March deadline look tight.
Other options being discussed include activating formal EU exit talks through a so-called statutory instrument or a resolution.
Both parliamentary mechanisms appeal to Downing Street because they avoid days of debates and amendments, but legal brains such as the former attorney general, Dominic Grieve, believe these options would not be legally sufficient.
David Davis, the Secretary for Exiting the EU, will update MPs on the case on Monday afternoon when he makes a statement reiterating the government's determination to win its appeal and stick to its March deadline.
Last week, Downing Street refused to say whether legislation was being drawn up for triggering Article 50 in case the appeal fails, stressing it was focused on winning the case.
While Mrs May has a majority in the House of Commons to push through Article 50, opposition MPs will press Mr Davis for more transparency over his closely held Brexit plans.
