The Wellcome Trust... Requires electronic copies of any research
papers that have been accepted for publication in a peer-reviewed
journal, and are supported in whole or in part by Wellcome Trust
funding, to be deposited into PubMed Central (or UK PubMed Central once
established). (Note that this requirement applies only to all grants
awarded after 1 October 2005, and from 1 October 2006 to all grants
regardless of award date.)
http://www.wellcome.ac.uk/doc_WTX031743.html