Brexit
The UK Supreme Court begins considering the lawfulness of Prime Minister Boris Johnson's prorogation of Parliament. It is jointly considering two appeals. One is against a ruling by the High Court under English law that the issue is solely a matter for the Prime Minister and one the courts do not have jurisdiction over. The other is against a ruling by the Court of Session under Scots law declaring the suspension unlawful and a nullity, and requiring Johnson to recall Parliament.
Sources: BBC News