100,000 criminals creating half of all crime.
40k p.a. to imprison them.
100,000 x 40,000 = £4Bln p.a.
The cost of crime in Britain is judged to be around £60bln p.a. and an inestimable cost in human suffering.
To me it is a no-brainer. Build the prisons and have a 3-strikes rule ending in a life sentence for habitual criminals who have absolutely no intention of living an honest life.
As I have posted on other blogs in the past, I am certain that with the right motivation, robust enforcement and the cutting down of the "social security hammock" the vast majority of otherwise low-level criminals would reform by themselves and lead an honest and useful life. They are currently, in effect, spoilt brats with no concept of boundaries.
This will leave a hard core of criminals who are beyond reform and the forces of law and order will have plenty of resources to deal with them.