The stipend is £14,790 (2012/13) per year.
Depending on how you meet the EPSRC criteria (
http://www.epsrc.ac.uk/funding/students/pages/eligibility.aspx.) you may be entitles to a full or partial award. A full award covers tuition fees at the UK/EU rate and an annual stipend of £14790. A partial award covers fees at the UK/EU rate only. The studentship is not available for candidates from outside of the EU.