In a report published today, the chief inspector of borders and immigration John Vine (pictured) found inefficiencies, inaccuracies and a lack of co-ordination in the Home Office's management of illegal immigrant records.
Mr Vine is highly critical of the contract signed with Capita to review the records of migrants in the Migration Refusal Pool.
He states "many of the expected financial and strategic benefits have not materialised", with far fewer migrants having been persuaded to depart than anticipated.
"Of the 120,000 people whose cases were sent to Capita for contact to be made, I found that less than 1% had left as a result of Capita’s intervention," he states.
He adds that the post-2008 Migration Refusal Pool has remained "almost static", standing at 173,562 at that time.
The report concludes: "The Home Office must make significant improvements if its strategy for reducing the number of overstayers is to succeed."
A spokesperson for Capita defended the contractor's handling of the contract.
"We reject the report’s claims that Capita has overstated voluntary departures," the spokesperson said. "We recorded departures, as with other processes, using a methodology agreed with the Home Office and these records have been and remain subject to rigorous scrutiny, quality assurance and governance."