The number of social media accounts shut down at the request of prison authorities has almost quadrupled in three years after hundreds of inmates used smuggled phones to post from behind bars.
Jail security officials took action in relation to material on platforms such as Facebook, Instagram and YouTube.
More than 1,700 accounts were removed from 2015 to 2018, statistics obtained by the Press Association show.
It is thought the bulk of cases were triggered by prisoners using illicit mobiles to upload content themselves.
Removals are also sought when video or images captured in jail, or messages sent from behind bars, are posted by people on the outside.
The Prison Officers Association warned the “shocking” revelations risk undermining confidence in the criminal justice system, while the Prison Service said it works closely with social media companies to close accounts used by prisoners.
Figures on social media accounts removed after being identified by HM Prison and Probation Service were released by the Ministry of Justice following a freedom of information request.
The number of removals increased in each of the four years for which data was provided, with 153 in 2015, followed by 462 in 2016, 527 in 2017 and 594 last year.
In total, 1,736 accounts were taken offline, with 1,121 – or nearly two-thirds – removed in 2017 and 2018.
The FOI response said the figures include, but are not limited to, accounts on Facebook, Instagram and YouTube.
The MoJ declined to provide a detailed breakdown of the cases by jail or social media platform as it could prejudice the prevention or detection of crime and maintenance of security and order in prisons.
Glyn Travis, of the Prison Officers Association, said: “The POA are not surprised by the shocking statistics which highlight the growing problems of prisoners using technology in prisons.
“The use of social media sites on illegal phones by prisoners can only undermine public confidence in the criminal justice system.
“These sites continue to be accessed and prisoners are taunting victims, intimidating witnesses and organising criminal activity from the safety of a prison cell.”
We do not tolerate the use of mobile phones in our jails and we work closely with social media companies to close accounts being used by prisoners… Any prisoner found with a mobile phone faces extra time behind bars
Alex Mayes, of charity Victim Support, said victims “may feel unsafe knowing that the perpetrator could potentially contact them or their family and friends”.
He added: “Victims should feel most safe when the perpetrator is serving their sentence and this news could leave them feeling that justice has not been fully served.”
A string of cases have highlighted the potential for images and footage captured behind bars to appear online.
In 2016 pictures said to have been taken at a prison emerged showing takeaway meals and steaks.
Last year Justice Secretary David Gauke spoke of his shock at videos posted on social media of prisoners under the influence of drugs.
Authorities have identified the illegal use of mobiles as one of the most significant threats faced by jails.
In the 12 months to March last year, there were 10,643 incidents where mobile phones were found in prisons in England and Wales, a 15% increase compared with the previous year.
Criminal gangs have deployed a range of tactics to exploit the lucrative contraband market behind bars.
Last month three dead rats stuffed with mobiles and drugs were found at HMP Guys Marsh.
A Prison Service spokesman said: “We do not tolerate the use of mobile phones in our jails and we work closely with social media companies to close accounts being used by prisoners.
“We are investing millions in body scanners, phone-blocking technology and other measures to prevent phones being smuggled into and used in prison.
“Any prisoner found with a mobile phone faces extra time behind bars.”
YouTube said it has a dedicated process for police and the prison service to flag videos directly to its teams for review, and takes action on videos and channels when it finds threats or violations of its community guidelines.