The estimate for building completion, at the time, was 2015 and the proposed extension would carry 24,000 people per hour, with a journey time of around 11 minutes to Bank and Leicester Square.
Further information from Battersea Power Station's September factsheet said "The NLE (Northern Line Extension) is currently proposed to be delivered in two phases, with the first phase to tunnel from Kennington to Battersea and creation of the new Battersea station, for an estimated cost of around £400m. The construction of the mid station at Nine Elms is planned to be the second phase, for an estimated cost of around £160m." However last week's pledge from Treasury Holdings put around £203 million towards the extension of the Northern Line (via Build.co.uk).
So where's the other £357 million (or whatever is actually needed) going to come from? At time of writing there's nothing from TfL or the Mayor to confirm any spend on a Northern Line extension, but it's probably too early to expect that.
As Nick Cuff said "There is still a great deal of work to be done but this is an important step forward". Watch this space for further news.