On first impressions this seems like good news. But, sadly, this is yet another of those occasions when first impressions are misleading. It took me a while to delve behind the numbers, but here is my understanding. An increase of 150,000 in the effective housing stocks may sound bigger than 118,000 completions but that first impression is misleading because those two numbers are calculated differently.
In 2010/11 the 150,000 increase in effective housing stock comprised 134,000 net additions and 16,000 empty homes brought back in to use. The government provides net additions data from 2004 onwards. They are calculated slightly differently from the figures used for the New Homes Bonus but the 129k figure for net addition in 2010/11 is close enough to the 134,000 figure reported by DCLG above to suggest the data are broadly comparable. Here is what those data show:
So the 2010/11 figures represent the worst net addition figures for the last five years. I think the government could argue that given the recession things may have been even worse without the New Homes Bonus (although the 08/09 numbers already capture the impact of the recession) and I think it would be reasonable to see what the numbers look like next year. But certainly the picture is much more worrying than misleadingly comparing completions to net additions.