NBC News' Ayman Moyheldin reports that the situation is unlikely to calm down in Egypt, describing the "sense of chaos" that has gripped the country.
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The PM will sound out the possibility of new free trade agreements with Gulf states for once the UK has left the EU.
In the unexpected announcement on Monday, Mr Key said it was the "right time" to leave politics.
As the Government's Brexit appeal comes to the Supreme Court, here's a look at what you need to know.