More than 2,500 prison staff have been subject to disciplinary action in the last five years, including for relationships with inmates, assaulting prisoners and racism, the Guardian can reveal, as the government prepares to launch a unit to tackle corruption in jails.

A total of 2,666 prison staff in England and Wales were subject to disciplinary action between mid-2013 and mid-2018, according to data released by the Ministry of Justice (MoJ) under the Freedom of Information Act.

The most common reason for disciplinary action was breach of security, which can include bringing drugs and mobile phones into prisons, with 960 workers subject to this charge.

Other charges included assault or unnecessary use of force against prisoners, for which 204 staff were disciplined, inappropriate relationships with a prisoner (64), racial harassment (19) and trafficking (28). There was also action over abusive language, sexual harassment and being unfit for work due to drink or drugs.

It is understood the Ministry of Justice will soon launch a counter-corruption unit (CCU) as the department battles with a fractious prison estate overcome with drugs, violence and poor mental health among inmates.

The formation of a counter-corruption unit was announced in the Government’s Prison Drugs strategy, which was published earlier this month.

The most recent figures show that in the year to March 2018 the number of incidents in which drugs were found in prisons increased to 13,119, up 23% from 10,666 in the previous 12 months. The number of mobile phone and sim card discoveries increased by 15% in the same period: there were a total of 10,643 incidents where mobile phones were found and 4,729 incidents where sim cards were found.

A lack of experienced prison officers has been blamed in part for the difficulties faced by the service. As of 31 December 2018, there were 22,722 prison officers in bands three to five, considered to be key operational grade in public-sector prisons, of whom 42% had less than three years’ experience.

In its response, the Ministry of Justice said: “The vast majority of prison officers and other staff carry out their duties to the high standards the public rightly expect, but the small minority who fall short of those standards are held to account.

“Allegations of inappropriate behaviour, though rare, are taken extremely seriously and are immediately investigated. We do not hesitate to take action where there is evidence of misconduct.”

The data released to the Guardian shows the prison service launched 6,597 investigations into misconduct between mid-2013 and mid-2018, including 2,270 into breaches of security, 718 into assault or unnecessary use of force against a prisoner and 174 into inappropriate relationships with prisoners.

A total of 567 officers were sacked in the same period, including 84 for breach of security, 68 for assault or unnecessary use of force against a prisoner and 39 for an inappropriate relationship with a prisoner.

The MoJ started to build its new counter-corruption unit last year after a root-and-branch review of how to tackle corruption within the prison service. It had hoped to launch in February but was delayed.

The counter-corruption strategy has four pillars that mirror the Home Office’s counter-terrorism approach: protect, prevent, pursue and prepare. The unit will prioritise “pursue” by providing support to prisons and probation to progress intelligence reports. The unit will have a small national team and larger regional teams.

Last year, the MoJ advertised for a head of the unit. It was expected the unit head would lead a team of 26 staff spread across the country.

In January, a prison officer, Jade Hicks, 35, was jailed after smuggling cannabis for an inmate she had befriended. Hicks, from Hemsworth near Pontefract, West Yorkshire, met the man when she worked at HMP Leeds.

In a separate case, Gemma Farr, from Draycott, Derbyshire, who worked in a prisoner rehabilitation role at HMP Dovegate in Staffordshire, was jailed for delivering contraband to prisoners.

Last year, Iain Cocks, a prison officer who had a sexual relationship with an inmate, was jailed for four years. Cocks, 51, had a relationship with the female prisoner for nearly two years at HMP New Hall near Wakefield, where his wife was also working at the time. Cocks, from Barnsley, South Yorkshire, had consensual sex with the inmate in a cell and a laundry room.

In December, two prison officers were jailed for assaulting a 17-year-old inmate at Wetherby young offender institution in 2016. Mark Burnett was sentenced to 15 months and Daniel Scott to 10 months. The teenager was being escorted through a corridor when Burnett shut the door to the exercise yard and said: “Do you think it’s funny to assault a prison officer?” Burnett, 50, who had been a prison officer for nearly 20 years, then punched the teenager in the face, and his colleague Scott, 28, also hit the inmate.

Prison officer sacked and jailed for having sex with inmate in cell Read more

Peter Dawson, the director of the Prison Reform Trust and a former prison governor, said misconduct among prison staff was “massively” damaging.

“Staff bringing drugs in is probably the easiest way of bringing a large quantity of drugs into a prison,” he said. “The more you tighten up other forms of getting drugs in, the more pressure staff will come under and the more they will look like the obvious way to achieve it.

“Prisoners generally if asked this question will say of course staff are involved and will probably identify corruption as one of the main routes of getting drugs into prison. It’s relatively low-risk, it’s relatively low-cost and you can bring in large amounts.”

He added: “Prisoners rely on staff to be honest in many ways. A corrupt member of staff is damaging because they will feed an alternative source of authority in the prison, they end up working for the prisoner, not the governor. Most prisoners don’t want that, they want the authorities to be in control. It’s massively damaging.

“It [corruption] is difficult to tackle. In terms of a new unit, we would welcome more attention on this. Corrupt staff are very dangerous to their colleagues as well as everyone else. Historically, the Prison Service has been reluctant to grasp this particular nettle.”