Jailed women 'vulnerable to abuse'
Women prisoners have been coerced into sex with staff in return for favours such as cigarettes or alcohol, campaigners said.
Assaults known as "decrotching", where women prisoners forcibly retrieve drugs from another inmate's vagina, are also thought to have occurred in jails, the Howard League for Penal Reform said.
The findings are published in the second briefing paper from the Commission on Sex in Prison, which was established by the Howard League.
The report recommends training and guidance for prison staff on how to support women, recognise bullying and identify relationships between prisoners.
Chris Sheffield, chair of the Commission, said: " Women in prison are particularly vulnerable and more likely than men to have a history of being a victim of violence or sexual abuse.
"It is important that policies recognise these differences and are developed in order to protect the vulnerable.
"It is equally important that staff in women's prisons receive specific training on working with women."
Some women form relationships in prison as a source of comfort and support, although some turn coercive or abusive, the Commission found.
The Commission also said women are at greater risk of entering prison with a sexually transmitted infection such as HIV.
The two-year Commission is looking at three broad themes - consensual sex in prisons, coercive sex in prisons and healthy sexual development among young people in prison.
A Prison Service spokeswoman said: "Sexual relations between prisoners are not common place. We do not condone sex in prisons or believe that prisoners in a relationship should share a cell.
"Reported incidents of sexual assault in prison are rare. Where an alleged sexual assault is reported or discovered it will be investigated and reported to the police if required."