The newly-appointed BBC Director-General Tony Hall said, "It takes a lot to drag me away from the Royal Opera House ... but the reason I stand before you today is that I care passionately about the BBC, about what it can do, it's programme makers and the impact we have in all different ways".
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.