Two staff at a privately-run immigration removal centre for women have been fired for engaging in sexual activity with a detainee.
A third employee at Serco-operated Yarl's Wood, in Bedfordshire, was also sacked for failing to take any action when the female detainee reported the two men, HM Chief Inspector of Prisons Nick Hardwick said.
It was reported last month that police were investigating claims that a 23-year-old Roma woman who was held at Yarl's Wood was subject to inappropriate sexual behaviour from guards.
But inspectors found no evidence that a "wider culture of victimisation or systematic abuse" had developed following the new allegations of abuse at the 400-bed centre.
– Nick Hardwick, HM Chief Inspector of Prisons
"We were concerned to find that two staff had engaged in sexual activity with a female detainee, something that can never be less than abusive given the vulnerability of the detained population, and these staff had rightly been dismissed."
Yarl's Wood holds mainly single adult women but also holds a number of adult families and there is a short-term holding facility for adult men.
Inspectors concluded that more female staff were needed urgently as there were not enough for a mainly women's establishment.
A number of women at the centre - where none of the detainees have been charged with an offence or held through normal judicial circumstances - were detained for long periods, including one for almost four years.
Elsewhere, the surprise inspection found pregnant women had been held without evidence of exceptional circumstances required to justify their captivity. One of the women had been admitted to hospital twice because of pregnancy-related complications.
And detainees who had clear human trafficking indicators - such as one woman who had been picked up in a brothel - had not been referred to the national trafficking referral mechanism, as required.
– Anna Musgrave, Refugee Council women's advocacy and influencing officer
"Some of the findings of this inspection are shocking.
"Women in immigration detention are extremely vulnerable, with many likely to be victims of gender-based violence, so we're horrified to hear that male officers enter women's rooms without permission.
"It's particularly disturbing that officials are not even following current policy and pregnant women are being detained without any clear reason.
"Pregnant women with insecure immigration status already have high-risk pregnancies and we believe they should not be detained under any circumstances. There is absolutely no excuse for compromising the health and well-being of a mother and her baby.
"This report shows that urgent changes are needed at Yarl's Wood to ensure that vulnerable women feel safe and that their dignity is respected."
Mr Hardwick added: "Yarl's Wood still holds detainees in the middle of a distressing and difficult experience and more thought needs to be given to meeting their emotional and practical needs.
"For the most vulnerable of the women held, the decision to detain itself appears much too casual."