Are prisons becoming more dangerous places?
At least 200 inmates were thought to have been involved in a "riot" at HMP Bedford.
The Prison Officers Association says warnings about violence in prisons are "coming to fruition".
This followed the death of a prisoner in HMP Pentonville, the third in England and Wales since the start of 2016. How dangerous are our prisons?
How many assaults were there?
Violence in prisons is on the rise, with assaults by inmates on each other and on staff increasing year on year.
There were 22,195 assaults across all prisons in England and Wales between March 2015 and March 2016.
This was the sharpest rise in the past decade, an increase of more than 31% in one year.
The prison population as at the end of March 2016 was just over 85,400, which was a slight drop on the same month the year before.
However, the rate of assaults has still increased.
The figure for 2015-16 was equivalent to 260 for every 1,000 prisoners. This compared with 198 in 2014-15.
The Chief Inspector of Prisons, Peter Clarke, has warned that prisons had become "unacceptably violent and dangerous places".
Are there enough staff?
The number of officers in English and Welsh prisons has fallen by a quarter in six years.
In 2010, there were 19,908 prison officers (excluding managers and supervising officers). By March 2016, the National Offender Management Service had 14,917 officers and by June 2016 this had fallen again to 14,690. And it now means the number of assaults of all types, whether prisoner against prisoner or against officers, now outnumber the staff who have to deal with them.
What's the situation at HMP Bedford?
There were 110 prison officers at HMP Bedford, in June 2016. This compared with 120 the year before.
The total operational staff is down from 180 to 171, including managers and supervising officers.
However, there has not been much fluctuation in recent years. In 2013, there were 110 officers and in 2014 there were 100.
The number of assaults did rise in 2015, with 100 in total, but this was still one less than in 2010.
How many people have died in prison?
In 2015-16, there were 321 deaths in prison custody. This is the highest figure for 10 years and 74 more than the previous year.
It works out at 3.8 deaths per 1,000 prisoners.
Five of the deaths were homicides, down from seven the year before.
Most deaths, 186, were put down to "natural causes" and 105 were "self-inflicted".
Where do most assaults happen?
The highest rate of assaults occurred at HM Young Offenders Institution Werrington, in Staffordshire.
In 2015, there were 360 assaults. The institution has a capacity of 142, meaning two or three assaults recorded for every inmate space.
How are prison staff affected by violence?
Assaults on staff in English and Welsh prisons were up 40% as well, with 5,423 incidents, compared with 3,887 the year before.
What was the situation in Pentonville?
HMP Pentonville, a Category B prison, recorded 50 serious assaults in 2015, a big rise on the year before.
However, the overall number of assaults was down. There were 421 assaults in 2015, 74 fewer than in 2014.
What's being done about prison violence?
The Ministry of Justice says it will recruit more prison officers, investing an additional £14m in 10 of the "most challenging" prisons.
Last week, Justice Secretary Liz Truss unveiled a White Paper detailing £1.3bn investment in new prisons over the next five years, and plans for 2,100 extra officers, drug tests and more autonomy for governors.