The government’s policy of making life intolerable for people who are suspected of illegally entering the UK is yet to show that it can persuade them to leave, Whitehall’s spending watchdog has found. The National Audit Office said that Home Office officials admit that they have no specific evidence to show the “compliant environment” policy – the successor to the “hostile environment” that led to the Windrush scandal – encourages voluntary departures or fosters compliance with visa and passport conditions. In a report issued on Wednesday, auditors also pointed out that the Home Office has not updated its estimate of the size of the illegal population for 15 years, and that nearly two-thirds of immigration enforcement detainees are released from detention without removal. It comes days after the equalities watchdog, the Equalities and Human Rights Commission, announced it would launch legal action to review whether the department had complied with equality law when implementing the “hostile environment”. Responding to the report, Meg Hillier MP, chair of the public accounts committee, said the department seems to have little information on which to base its policies. She said: “The Home Office has no idea how many people are in the country illegally and doesn’t seem interested in finding out. “It can’t demonstrate that its actions to control illegal immigration are working as intended, and doesn’t understand how different aspects of its work fit together.” The report into the Home Office’s immigration enforcement directorate examined its compliant environment policy, which limits access to work, housing, benefits and other government-funded services. But auditors said there was no evidence that it encouraged compliance among those staying in the UK without documentation. “The department acknowledges that it had no specific evidence base to support the effectiveness of these measures when they were introduced. It is currently unable to measure whether these activities have the desired effect of encouraging people to leave voluntarily,” the report said. The last estimate of the size of the illegal population in the UK was made in 2005 and suggested there were about 430,000 people in the country with no right to remain here, auditors said. The department has instead estimated that demand for immigration enforcement activity is between 240,000 and 320,000 cases per year, added the report. Nearly two-thirds of immigration enforcement detainees are released from detention without removal, the report found, with greater numbers of detainees being released at a late stage because officials could not deport them. “We have not seen evidence it has tried to actively understand and manage these challenges and it has no strategy across the work of Immigration Enforcement and the rest of the Department to reduce their frequency. “In the 12 months to the end of December 2019 it released 14,900 (62%) of the detainees whom it intended to remove from the country,” the report said. The “hostile environment” label was dropped two years ago after the Windrush scandal revealed that thousands of people who came to the UK from the Commonwealth were denied access to public services and jobs – with some dying abroad after being deported. The then home secretary Sajid Javid disowned the term in favour of “compliant environment”, and vowed to prioritise the Windrush scandal. But many campaigners and politicians have claimed that the new policy is a continuation of the same core principles.