Women held at a controversial immigration removal centre are increasingly handcuffed for hospital visits, a report indicates.
Newly published figures suggest the practice has become more frequent since the Home Office raised the penalty for detainees absconding from Yarl's Wood under the terms of a new contract.
The facility in Bedfordshire, which has a maximum capacity of 410, is the main immigration removal centre for women in the UK.
It has repeatedly come under scrutiny since it opened in 2001 and was last year labelled a "place of national concern" by the prisons watchdog.
Management arrangements of new contracts for the operation of Yarl's Wood were examined by the National Audit Office.
Serco has run the residential services under contract to the Home Office since April 2015 and G4S has run the health services under contract to NHS England since September 2014.
In some instances, the Home Office's decisions about the contract had a "negative impact" on vulnerable residents, the NAO found.
In the new contract the department significantly increased the penalty for residents absconding and now requires Serco to escort residents to out-of-area hospitals which are unfamiliar to staff.
Home Office guidance states there is a "presumption against" the use of handcuffs during visits to outside facilities, the report said.
It added: "Although no resident has ever absconded on a hospital visit, Serco told us that it is now more likely to use handcuffs due to the combination of more risky hospital visits to unknown hospitals and the much higher penalty if a resident absconds."
Three per cent of women were handcuffed for hospital visits between October 2014 and April 2015 - a figure which rose to 11% for the same period the following year, when the new approach had been implemented, the report said.
It added that the Yarl's Wood Independent Monitoring Board (IMB) found that some residents have refused to go to hospital visits as they find the practice of handcuffing humiliating.
While a move to "self service" in the residential services contract reduced demands on staff time, Serco's reduction of staff meant there were "insufficient operational and management staff", according to the report.
It said the contract envisaged freeing up staff time by moving to a 'self-service' model where, for example, residents send their own faxes and book their own visits. Serco has now made further changes to the staffing model and replaced some of the posts that were removed.
Meanwhile, G4S was said to have been slow to meet its contractual obligations for training. NHS England brought healthcare expertise but did not have a good understanding of the particular needs of residents when it designed the service specification, the watchdog found.
However, it said there has been some "significant progress" at Yarl's Wood, including improvements to healthcare facilities, the gender balance of operational staff and adult safeguarding.
Amyas Morse, head of the NAO, said: "It is important that services for vulnerable people, like those at Yarl's Wood, are delivered 'right first time' and this did not happen at Yarl's Wood. We do though give credit for the work that is now taking place to address the problems."
Julia Rogers, Serco's managing director of immigration, said: "The NAO recognises that there has been significant progress at the Centre since the various independent reviews were published over the past 18 months and also highlights that none of them found evidence of a culture of abuse.
"The report also highlights that the Lampard review found that most residents were largely positive about their relationship with staff' as well as reporting positively on a number of aspects of the Centre.
"The NAO's report contains ten key findings, which we welcome and we have already addressed the three that are directly relevant to Serco, including improving training for our staff, increasing the number of staff and working with others at the Centre to improve 'wrap around' care.
"We understand and appreciate the vulnerability of the people in our care and the legitimate concerns that many people and organisations have about them and we will continue to work to ensure that they are well looked after at this difficult time in their lives."