My understanding is that your 8% increase is in regard to the increase in official development assistance. The bill in question is talking more specifically about a very small subsection of this expenditure, which does not grow at 8% a year. It's actually our decision to take part in this initiative, which was announced in Gleneagles in 2005, to basically compensate the World Bank and the IMF for debt relief they provide to countries.
On October 27th, 2009. See this statement in context.