The British prime minister has lost a Supreme Court appeal over how the UK can leave the European Union.
It means MPs in Westminster will have to be given a vote before Brexit can begin.
But it also says the devolved governments won't get a say - which could spark another push for Scottish independence.
Our political correspondent Gavan Reilly reports:
Meanwhile the Labour leader says Sinn Féin should consider taking its four seats in Westminster ahead of its vote on Brexit.
Sinn Fein holds four seats in the House of Commons but has never taken them up, as they would have to swear an oath to the crown.
But Labour's Brendan Howlin says the matters at stake are so high, the seats should be taken up:
