A decision to give a private security firm a new eight-year contract to run a women's detention centre has been criticised by refugee groups.
The government has announced a £70m deal for Serco to manage Yarl's Wood in Bedfordshire.
In 2013, two guards were dismissed for inappropriate sexual conduct, but claims of a sexual assault in 2011 were not substantiated.
Serco said it was planning a range of improvements following inspections.
The firm took over the running of the immigration 410-space removal centre at Milton Ernest near Bedford, in 2007.
Last year, two members of staff were fired for engaging in sexual activity with a detainee, while a third employee was sacked for failing to take any action when the detainee reported it.
Investigations by Serco and Bedfordshire Police concluded the sexual assault allegation could not be substantiated.
Natasha Walter, of Women for Refugee Women, said the charity was "more than disappointed" about the contract.
"Serco is clearly unfit to manage a centre where vulnerable women are held and it is unacceptable the government continues to entrust Serco with the safety of women who are survivors of sexual violence," she said.
The Home Office said there had been a "comprehensive re-tendering process" for the new contract.
A spokesman said: "Serco's bid demonstrated its offer was the best in meeting quality and cost criteria and providing value for money for the taxpayer."
Louise King, a Labour councillor at Bedford Borough Council, said: "A detention centre by its very nature does not deliver value for money - it costs in excess of £120 per person per night to detain often very vulnerable people, for indeterminate periods, in a setting that it would appear is detrimental to their health and wellbeing.
"We need to be looking at alternatives to detention."
James Thorburn, Serco's managing director for home affairs, said: "We know the people who are in our care are at a difficult stage of their lives.
"We understand the challenges of looking after vulnerable and concerned people and we recognise the responsibility we have in managing the centre in a caring and efficient manner."