The crowd was also played a video message from former England captain David Beckham.
After the Government committed to giving an extra £375 million to help feed the world's poorest children, Beckham said:
We've had good news. Earlier today the Prime Minister met with other world leaders and has made a real commitment to ending child malnutrition and hunger. There is more to do though and you can help.
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Temperatures will be on the rise in the next few days, with highs of 25C in the sunshine by Thursday, but do not expect clear blue skies.