“Mini riots” are breaking out in prisons across England and Wales as overcrowding sends lags barmy.

Boffins say the current capacity crisis has increased the risk of large-scale disorder despite an emergency early release scheme being introduced.

The shock news comes just a day after it was revealed prisons are just days away from being full with an emergency “one-in, one-out” system set to be rolled out codenamed Operation Brinker.

Prisons bosses fear if a full riot breaks out and jails are put out of use, there would not be enough space elsewhere to detain and separate the displaced convicts.

Police cells could be used to hold inmates amid fears the crisis could endanger the safety of prisoners, staff and the public.

Mark Fairhurst, the national chairman of the Prison Officers’ Association, said that “concerted indiscipline”, which can cover incidents from groups of inmates defying officers’ instructions to violent brawls, were soaring.

He added: “They can be mini-riots, we’re running at one per week.

“They’re happening all over the place and it’s far more than normal.

“All the catalysts for major disturbances are happening, and if we lose a wing or a jail [to a riot], where are we going to put the prisoners?”

There are only about 1,400 spaces left in prisons in England and Wales, but the Prison Governors’ Association estimates that there are only 700 in adult male prisons, because the larger figure includes women’s jails and open prisons.

A spokesman for the Prison Service said that robust plans were in place to deal with disturbances, including specially trained Tornado response teams.

He added: “We have a zero-tolerance approach to violence and prisoners who break the rules will be punished.”