A former Serco official who worked at the UK's Yarl's Wood immigration detention centre has spoken out about "endemic" anti-immigrant sentiment among staff and repeated sexual abuse at the facility.

The whistleblower, who resigned from the private outsourcing company last year after raising his concerns, said vulnerable women were deported without their mental health being properly assessed.

He also detailed a case of a detainee with profound psychological issues being sexually assaulted.

"The lack of engagement with mental health in relation to assessment and safeguards was very concerning," the former employee told the Observer.

"They weren't doing assessments to rule out mental health. God knows how many people they had deported without a proper assessment.

"Officers would say openly: 'They need to go back, they need to leave the country, they're only coming here to use NHS resources,'" the whistleblower added.

"A common phrase was: 'They're only putting it on to block their removal.' I've actually heard [senior staff] say: 'These people are putting it on.' It was endemic...even the senior management structures were saying this, it was a mindset."

The whistleblower, who is the first senior employee to have broken ranks since the detention centre opened in 2001, corroborated allegations from former detainees that some women felt they had to flirt with staff in order to obtain everyday essentials such as toiletries.

He also claimed that a female Serco officer informed him of a "blind spot" inside Yarl's Wood which was not covered by CCTV and was a well-known location for sexual encounters. The area was where an officer had previously made a female detainee pregnant.

"She said: 'This is a blind spot, this is where people come.' They seemed to know where all the blind spots were."

The whistleblower estimated that more than half of the detainees at any one time - over 200 individuals - had either self-harmed or were at risk of self-harming.

He said one of the incidents he witnessed involved a women pouring boiling water over herself. She was left in a state of shock for hours. Another woman tied a ligature around her neck while she was apparently under observation.

Norman Abusin, Serco's director at the detention centre, told the Observer: "We absolutely refute the suggestion that there is an endemic culture of disbelief towards the women in our care at Yarl's Wood.

"We feel that such general allegations are unfair to our hardworking and dedicated staff. The wellbeing of the people in our care is always top priority."

A Home Office spokesman added: "Yarl's Wood is inspected regularly by the Chief Inspector of Prisons, as well as its independent monitoring board. Neither have found any evidence pointing towards a 'culture of disbelief' at the centre."