Locking up individuals where you are put next to more criminals, where you are under threat, where you have to keep proving your credentials in the prison society is also not likely to work, and the larger the prison, the more this problem is reinforced since there is always another prisoner who you have to encounter.
Large prisons make control far more difficult, because what you have is a social system, it makes the job of the rehabilitator far harder, because you become one lone voice in a sea of criminally opinionated chancers.
The US is well known for its very large prisons, and the UK has moved toward that direction in closing smaller prisons, and is currently in a program of building some very much larger ones, 2500 place prisons is very large for the UK and that is what is currently under construction
The justifications for this are things such as greater scope for efficiency savings - well the issue is that the ‘efficiencies’ are merely operating costs instead of the real savings to be made from rehabilitation, and I have yet to see any evidence that larger prisons will actually improve rehabilitation rates - quite the contrary, I have seen evidence that smaller prisons are more effective, and we have the US experience of large prisons where rehab rates are woeful and that it leads to higher prison populations.
Another justification is that lots of UK prisons are old, and this leads to them being expensive to operate and that conditions are generally bad - however like any structure, lack of maintenance, repair and investment will inevitably result in run down prisons, and its no wonder at all that conditions are poor.UK prisons, like much of our public sector have undergone ideologically driven cuts in funding for at least the last 8 years, and this is in line with lots of the neoliberal view of the world where costs are driven down to the minimum by privatisation.
Its worth noting that in the US, that Feds have finally understood that you cannot have prisons on the cheap, and is withdrawing support for private prisons - I realise that entails just the federal prisons which is a minority of the total prison population but someone somewhere in the US has started to question the privatisation mantra for public services
The thing that undermines the US style large prison is that evidence does show that prisoners who maintain links with their families, especially drug users, are more likely to be rehabilitated, yet larger prisons means fewer of them, meaning they will be far more geographically spread out and this means less family contact.
Everything we have borrowed from the US has increased our prison population, whether its is cost cutting, larger prisons, reform programs.
If you want to reform prisoners, or have any sort of control over any sort of population, what you do is reduce the impact of peer pressure - and that means reducing the numbers in each cadre - so a smaller prison will be better controlled than a larger one, and you have more staff with more influence both in direct control but also so that they have more scope to implement their own initiatives, instead of having large prisons controlled centrally from a ministry in London