My first experience of campaigning was volunteering for the Freedom from Hunger movement as a schoolboy.

My older brother ran a small newspaper to raise money for Oxfam's charity appeal – and I helped him.

We billed it as the only paper whose proceeds were devoted exclusively to helping the hungry.

As an 11-year-old I believed then what I believe now: that in a world so productive and fertile it shames us that so many still face a daily struggle to feed themselves and their families.

In the 1960s when I was first galvanised by this injustice and inspired by the example of President Kennedy, almost 40 per cent of the world's population went hungry. For 40 years we made steady progress and reduced the numbers underfed to 15 per cent of the world's...