Wikipedia doesn't mention any required disclosures, but mentions the Charity Comission which links to Intelligent Giving which merged with New Philantropy Capital.

FHI doesn't show up in the CC, NPC, or Guidestar, so I went a little broader afield and tried a site search on the FHI website: budget site:fhi.ox.ac.uk. This immediately turned up FHI's own documentation of its activities and budgets, a 2007 'annual report'; I used part of its title as a new Google search: future of humanity institute achievements report. These seem to be what you want:

1. 2005-2007
2. 2008-2010

(That wasn't so hard, was it?)