Perhaps I've missed something obvious when reading various websites that discuss these grants but are they per year or one grant for the full duration of the PhD? To clarify, I'm talking about the EPSRC stipend which for the year 08/09 was £14,400.

A grant runs for the duration of the PhD, or at least enough years to complete it all going well. I had an EPSRC grant over a decade ago.

Ok, thank you. One other question, do you receive the same amount each year or does it increase with inflation? E.g. if you started this year would you get £14,400 each year or would you get a slightly higher amount due to inflation?

The amount increases each year.