Overstay migrant data 'inaccurate'
The number of immigrants who have overstayed their visas has surged following the discovery of tens of thousands of further files.
Inspector of borders and immigration John Vine said the overall size of the so-called migration refusal pool (MRP) - the number of foreign nationals who overstayed their visas in the UK after 2008 - was 173,562 in the three months to June this year, compared to 174,057 in the same period two years earlier.
But Mr Vine was informed at the start of his inspection of the existence of a further 223,600 records, pre-dating December 2008, which had not previously been included within the pool.
By January this year, the pre-2008 records had been reduced to 168,300.
He said: "Any failure to take action against foreign nationals who overstay their permission to be in the UK has the potential to undermine public confidence in immigration control."
The Home Office signed a contract with outsourcing giant Capita to review and, where possible, close the records of migrants in the migration refusal pool.
But Mr Vine found this move had not fulfilled most of the benefits that the department had claimed would result.
The overall number of post-2008 records in the pool had fallen by only 3.6% between April 2013 and April 2014 and there was no evidence that Capita's work had increased the number of enforced removals that the Home Office had been able to achieve, the inspection said.
In addition, less than 1% - 880 - of those overstayers who had passed through the Capita contact management process had departed after contact.
The inspection found there were "significant inaccuracies" in Capita's classification of migration refusal pool records.
It found that 16 of a sample of 57 records which were closed because the migrant had been discovered to have left the UK were completed in error.
The inspectors estimated that, as a result of this, departures could have been overstated by more than 1,140 in 2013/14 - more than a quarter of the total of 4,080 claimed by Capita in that year.
Mr Vine added: "I was disappointed to find a high level of inaccuracy in the classification of MRP records, with more than a quarter of departures in my sample being incorrectly recorded.
"Considerable improvements in the Home Office's capability to monitor, progress, and prioritise the immigration enforcement caseload will be needed to deliver its strategy for reducing the level of irregular migration."
Mr Vine also said Capita had only managed to save the public purse £4.2 million in 2013/14 - compared to an anticipated £18 million for the year.
Shadow home secretary Yvette Cooper said: " This is part of a disgraceful catalogue of chaos from Theresa May over border control - including giving British citizenships to killers and criminals, failing to deport foreign criminals, a 'no ifs, no buts' net migration target in tatters, and an attempt to deceive Parliament over the European arrest warrant.
"Why won't she conduct a full review of the criminals given citizenship, and follow Labour plans to introduce 1,000 additional enforcement staff, proper entry and exit checks?
"Too often, Theresa May fails in her responsibilities on border control, then runs and hides rather than sorting the problems out."
Immigration and security minister James Brokenshire said: " We inherited an immigration system in complete disarray, which turned a blind eye to hundreds of thousands of people with no right to be here, and made no attempt to remove them or even to properly identify the scale of the problem.
"Under the UK Border Agency there was no systematic plan to deal with illegal migrants other than failed asylum seekers and foreign criminals.
"We scrapped the failing UK Border Agency and brought its work back under the control of ministers partly in order to sort out that mess.
"New powers in the Immigration Act are restricting access to work, housing, benefits, healthcare, bank accounts and driving licences of illegal migrants, making it far tougher for those with no right to be in the country to stay here.
"We are committed to building an immigration system which is fair to British citizens and legitimate migrants and, as this report makes clear, applying a rigour to the immigration system it has been lacking for many years."
A spokeswoman for Capita said: "Capita performs only part of the process - contact management and some parts of the casework process.
"It is not contracted to handle, nor able to effect change in, the end-to-end process.
"The processes Capita followed - in terms of classifying data and reporting statistics - were set out and authorised by the Home Office.
"Both processes and outcomes were then subject to rigorous and ongoing scrutiny, governance and quality assurance."
She added: "We reject the report's claims that Capita has overstated voluntary departures. 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."
Keith Vaz, chair of the Home Affairs Select Committee, said: " I am glad that the Home Secretary has acted on the committee's request, made to her on Monday, to publish this report. However, it makes for deeply disturbing reading.
"To fail to know the whereabouts and precise numbers of thousands of people who have no right to stay here is a serious indictment of our immigration system and it makes a mockery of claims that our system works.
"Capita's contribution has been minimal, but it costs the taxpayer millions. The total of the 'disappeared ones' is now the size of a small English city."