For England and Wales, average completion time is 25 months which breaks down as:
- 10 months from obtaining permission to starting on the site
- 15 months from starting to completion
- 1 months to start
- 8.5 months start to completion
- 1 month to start
- 11 months start to completion
In short, the international comparison doesn't seem to get us much further other than to show that i) we are slow to start and that ii) in the US at least, as regulations increase, it takes developers longer to complete.
Either way, simply pointing to the headline figures for England and Wales of 400,000 permissions 'unimplemented' and average completion times of 25 months doesn't tell us much about the source of any problem and what we might do about it.
[NB: If anyone knows of something more systematic on this, I'd be happy for pointers.]