Today lawyers for campaigner Raymond McCord and anti-Brexit politicians including SDLP leader Colum Eastwood and Green Party leader Steven Agnew will join the Supreme Court hearings as the British government appeals against the need for Parliament to vote on triggering Brexit.
The case is due to finish on Thursday with a ruling in the new year.
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Your key questions about the Brexit Supreme Court case answered
Day Two: Northern Ireland Attorney General John Larkin speaks to the court
Who's who in the Supreme Court
Everything you need to know about the Brexit case at the #SupremeCourt