> The private sector has been building 200,000 units a year [...] we used to build enough houses. The difference is that in addition to the 200,000 privately built housing units we used to have 200,000 units of government built housing a year.

Right, so government stopped building public housing, but didn't allow private sources to fill the gap. That seems clear enough.

> This report from local governments shows that around 50% of granted planning permissions are still waiting to be built.

That's not at all what that report says. Again, in the past 10 years permission has been granted to build over 2 million homes; the overwhelming majority have been built. Planning permissions are the most critical input in the house building process; of course builders keep an inventory on hand. That inventory ballooned a bit during the crisis; as your own link notes, it's now falling again, and only amounts to about a 12 month supply.

> Additionally it says that councils approve 9/10 planning permissions

The existing rules are pretty clear, and obviously people don't apply for permissions which they know will not be granted. I mean, this entire thread is on the context of loosening restrictions; you're surely not claiming that 90% of applications to build in the greenbelt would be granted?

What would be relevant - and what is crucially NOT in your link - is evidence that there are building sites for which planning permission would be granted, if anyone applied, but for which no one is applying. But what seems to be the current status (and which your link supports) is that the supply of building sites for which permission can be obtained is about 200k/year, of which the overwhelming majority are 1) applied for and 2) built upon.