The Government's £220m school meals pledge has been described as inadequate by the outgoing chair of the School Food Trust, Dame Suzi Leather.
She said spending had to rise by 40% in primary schools from the new minimum of 50p per meal to 70p. The figure should be 80p rather than 60p in secondary schools, she added.
But she denied that her departure was linked to the issue of underfunding. She said: "There is no connection at all. In my new role as chair of the Charity Commission there would be a conflict of interests with the School Food Trust."
Vice-chair Maggie Jones, who is director of policy and public affairs at trade union Unison, will take over until a permanent replacement is found.