THIS IS THE NEW ARMORGROUP BB!!!

Purely from a technical point of view - the personnel on PMCs books will tend to be ex-military, with experience of protection/security/defensive operations. Prison staff are trained to guard the prisoners in a different way. The rates of pay the PMCs staff get would deter the PMCs from moving into this area with the current staff, so they would have to employ trained civilians to do the guarding/prison type jobs. This would involve a whole new expenditure route.

Personally I can't see it. The biggest deterrent would be the lower margins, but the stink caused by employing a PMC to take-over prsion/probation would be huge. There's getting tough on crime and criminals, but employing ex-special forces to guard prisoners would give out the wrong signal!

Like your lateral thinking though...