Housing numbers part 2

I wrote yesterday that I found the housing numbers a little confusing. CLG have kindly provided clarification. So, here goes:

Existing commitments (i.e. before Monday 29/06)
Affordable housing provision (completions) for 09/10 & 10/11: 90,000
Cost 09/10&10/11: £6.4bn

The "housing pledge" gives:
Additional affordable housing starts 09/10 & 10/11: 20,000 with completions not later than 2011/12.
Additional expenditure: £1.5bn in 09/10&10/11 and the remaining £0.6bn in 2011/12 (for a grand total of £2.1bn)

I haven't tried to figure out the details of how the extra £2.1bn is funded.