Last month Britain confirmed its intentions to build three so-called Titan prisons, each holding 2,500 inmates.
Fleury-Merogis holds 3,800 prisoners
BBC Home Affairs Correspondent Danny Shaw reports from Europe's largest prison - the 3,800-strong Fleury-Merogis near Paris - on how super size prisons work in reality.
As you walk into the main courtyard of maison d'arret de Fleury-Merogis, you would be forgiven for thinking you had stumbled into a grim 1960s housing estate: grey concrete walls, walkways, narrow windows and patches of grass.
But look up, and there is a watchtower, with an armed guard keeping look-out.
Wires criss-cross the tops of buildings - to stop helicopter escapes - and at the bottom are piles of rubbish, tossed from their cell windows by prisoners.
The sheer size of Fleury-Merogis adds to the impression of a bleak and desolate place: it occupies 180 hectares, and is split into three sections - for women, juveniles and men.
The sprawling men's block holds around 2,500 prisoners - which itself is bigger than any jail in Britain.
The first section of prison to be built in 1968, the men's block is divided into five units, each of which contains three wings, four storeys high.
Staff say because the prison is split into separate sections, it is easier to manage, than if everything was in one gigantic building.
But the men's block feels as if it is a machine; together, the units form a kind of circle - each wing like spokes in a wheel.
The outdoor facilities - including a sports field - are a plus point, until you remember that some 3,800 people will want to use them.
And they all need to be supervised. It is not like a relaxing Sunday at the park.
Inside, the prison appears to be clean and well-ordered.
But the cells I saw were showing their age, with rusting window frames and potentially dangerous sharp-pointed wooden fittings and ligature points.
By 2012, I was told, they will all be re-fitted, as part of a 400 million Euro upgrade. It cannot come soon enough.
The most impressive thing about Fleury-Merogis were the staff.
Working in difficult conditions, dealing with prisoners from 80 different countries, they appeared to me to be courteous, friendly - and disarmingly honest.
One senior officer, Bernard Gaudicheau, told me about the difficulties of managing large groups of inmates - they are "bolder" and "feel stronger", he said.
Unlocking a cell with one or two inside is very different from having three or four behind the door.
When I asked him to list the advantages of Fleury-Merogis, the pause was as long as a prison van.
But there was no delay when I asked Mr Gaudicheau if he judged the prison a success or failure. "Echec," he replied. Failure.
Because Fleury-Merogis is what in England and Wales would be called a "local" prison, housing prisoners for up to a year, on remand, during their trial and immediately after sentence, there is not much time for officers to cement relationships with them.
The problem is made worse in a big, impersonal jail, with a rapid staff turnover.
Officers also complain that there is no time for prisoners to learn skills or languages - 35% are from outside France.
Prison officials told me the record on disorder, self-harm and suicide compares favourably to other jails.
But I was struck by the number of prisoners allowed out for exercise together - a recipe for trouble.
Some of the prisoners were huddled together in the shadows, while others prowled under the walkways, out of sight of the officers on look-out duty.
The governor, Joaquim Pueyo, admitted that group activities in the courtyard can sometimes be hard to manage.
Some prisoners refuse to go out, some are too scared, he said. New CCTV cameras will help.
The acid test of whether a prison works is whether the governor would recommend it to others.
So, sitting across a boardroom table at his office in the administration block, I put the question to Mr Pueyo: if British Government ministers sought advice on the prison building programme, what would he say?
His brow furrowed and his eyes focused on the table. "Six cents places," he said.
The maximum number of places should be 600 - that was his recommendation.
This, by the way, is the size of prison the French are now building to tackle their own overcrowding crisis.
In France, at least, there will be no new jails like Fleury-Merogis.
Hear the full story on BBC Radio 4: File On 4 Tuesday 18 March 2008 at 2000 GMT, repeated Sunday 23 March at 1700 GMT or online at the File on 4 website.