Has Brexit now happened and has the UK left the European Union?
No. The UK is still a full member of the EU. What has happened with Theresa May signing a letter to the European Council is that the formal two-year process of leaving the EU has started. There will now be months of negotiations to agree terms, and the final deal will be voted on by the UK and European Parliaments for ratification.
What did the Tottenham MP David Lammy say about the fire in Kensington?