Image copyright Getty Images Image caption Justice Secretary David Gauke said violence and self-harm in prisons is "unacceptably high."

The number of assaults in prisons in England and Wales has reached a record high.

There were 33,803 attacks by prisoners in the year to the end of September 2018 - 20% up on the previous year.

The figures include a record 10,085 assaults on prison staff - up 29%.

There were 92 self-inflicted deaths in 2018, up from 72 in 2017.

The charity Prison Reform Trust described the figures as "disturbing".

Of the total number of assaults 3,949 (12%) were serious, up 6% from the previous year.

The figures, published by the Ministry of Justice (MoJ), also revealed there were:

325 deaths in prison custody in the 12 months to December 2018 - up 10%

24,138 prisoner-on-prisoner assaults in the 12 months to September 2018 - up 18%

Four killings in jail last year

Many prisons in England and Wales have seen surging levels of violence, drug use and self-harm in recent years.

The government says it is spending an extra £70m, including recruiting 4,000 extra staff, to help boost security in prisons.

Ministers plan to roll out synthetic pepper spray, known as Pava, to staff in publicly run prisons for men this year, following trials.

The MoJ has also announced traditional prison window bars are to be replaced with toughened glass and air vents in new prisons to help prevent drugs being smuggled in.

Justice Secretary David Gauke said he was "optimistic" the new measures could reduce violence.

He said: "Clearly there is huge amount yet to be done but I am determined to cut the violence so prisons can focus on rehabilitating the offenders who will be back out at some point."

'Making a volatile situation even worse"

Mark Day, head of policy at the Prison Reform Trust, said government plans were not working and warned Pava sprays could make "a volatile situation even worse".

"The measures the government have put in place to improve prison safety, including increasing staff numbers and the roll out of a new key worker model, have not yet succeeded in reversing this rising trend."

Prison staff union the Prison Officers' Association said the figures were shocking and showed no progress had yet been made.

Analysis: Ten prisons

By Danny Shaw, BBC home affairs correspondent

Image copyright PA Image caption Prisons minister Rory Stewart has put his job on the line

Prisons minister Rory Stewart has promised to resign if there isn't a reduction in violence in 10 of the worst-affected jails by this summer.

Mr Stewart made his pledge in August last year when a programme of investment began in those jails to provide them with extra staff, scanning equipment and training.

A BBC analysis of the assaults data shows the huge scale of Mr Stewart's mission - and some early, tentative signs that it may be working.

In the 12 months to the end of September 2017, there were 3,444 assaults in the 10 prisons.

In the following 12 months, there were 4,366 assaults - an increase of 27%, which was above the average rise across all prisons of 20%.

The largest increases were at:

HMP Lindholme, South Yorkshire - assaults more than doubled from 244 to 577

Isis Prison, south-east London - they went up by more than two thirds

HMP Humber - recorded a 60% rise

Assaults fell in only one of the 10 prisons - Wormwood Scrubs in west London.

However, comparing the first two months of the 10 Prisons Project - August and September 2018 - with the previous two months, there are some more positive signs.

There were 800 assaults in the 10 prisons in June and July 2018. That number fell to 768 in August and September, a 4% reduction. Seven of the 10 prisons recorded a drop in assaults.

It is far too early to draw firm conclusions from the data, but it does give Mr Stewart some grounds for optimism that his job may be safe - though there's a long way to go.