Chief Secretary to the Treasury Danny Alexander has told ITV News the fall in inflation is a "welcome relief" for families who have been under financial pressures in recent years.
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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.