Please note that though the link Katie just supplied with the CC's guidance on "The Advancement of Education for the Public Benefit" is relevant to the theoretical issue, we are not actually now applying under that heading but under one of general public utility, so it is the general guidance http://www.charity-commission.gov.uk/Charity_requirements_guidance/Charity_essentials/Public_benefit/pbsummary.aspx on the CC website that is directly relevant, and the three parts of Principle 1. I can't say much more, as I'm not in a position to share the correspondence with the CC .
In addition to the items mentioned, academic studies or high-quality press stories on the Wikimedia projects' impact in the Third World would be helpful - we have Wikipedia for Schools covered.
Please add anything unearthed at the page here: http://uk.wikimedia.org/wiki/Charity_status_application/help_wanted
Thanks,
John