David Cameron insisted aid spending made him "proud to be British" today as he urged more investment to tackle global hunger.
Hosting a conference intended to drum up money for the developing world, the Prime Minister backed a target of saving 20 million children from chronic malnutrition by 2020.
Bill Gates and Danny Boyle are set to address the protest rally to coincide with the London meeting, which preceeds the G8 summit in Northern Ireland.
The demonstration, hosted by lobby group Enough Food For Everyone If, is expected to attract thousands to Hyde Park.
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David Cameron said the Met proved it can "do more with less" and declined to criticise the Mayor of London for his water cannon spend.
A group of disabled activists threw toys and balls at him as he entered the conference.
A wet start to the week and the unsettled weather is set to continue over the next few days.