Kate McCann, Telegraph, June 15, 2017

Up to 250,000 people drop off the radar and end up as illegal immigrants in Britain every year, according to secret Home Office figures, amid warnings that border controls are completely ineffective and will only get worse after Brexit.

David Wood, who was head of immigration enforcement at the Home Office until 2015, said that more than 1.2 million illegal immigrants are currently living in Britain, predominantly after overstaying their visas.

People are not aware of the scale of the problem because official figures are not published and Home Office estimates for illegal immigrants are kept secret by ministers because they are “embarrassing”, according to experts.

In a highly critical paper for Civitas, written with Alasdair Palmer, a former Home Office speechwriter, Mr Wood disclosed that the Home Office has privately estimated that between 150,000 and 250,000 foreign nationals fail to return to their home country when they should.

They include people who come to the UK illegally in the back of lorries, those who are refused asylum (around 26,000 last year) and students and others who overstay visas.

But the true numbers are not recorded officially because the Government’s new e-borders system does not share data with the Office for National Statistics and others, leading to inaccurate figures that are as good as “guesses”, they said.

Mr Wood and Mr Palmer said: “It is understandable that the Home Office should have kept those estimates to itself: they are politically extremely embarrassing.

“Large numbers of illegal immigrants are a clear indication that immigration policy is not having the effect it is meant to”, they added, and ineffective controls “can be worse than no immigration controls at all” the researchers found.

They warned that because Government policy does not take into account the hundreds of thousands of illegal immigrants living in the UK: “Not only does it fail to reduce the number of foreign citizens settling in the UK, it also ensures that a very high proportion of them will not pay taxes and will be involved in illegal activity”.

The researchers, both highly experienced Home Office staff, added it is “obviously wrong not to release the estimate of the number of illegal immigrants to the public”.

They said: “They are a critical element in the debate on immigration. Keeping them secret may save ministers from embarrassment. But it makes proper policy planning impossible.”

The researchers also called on ministers to use National Insurance Numbers to estimate immigration instead, which show there were 827,000 foreign citizen registrations in 2015 alone. By contrast, over the same period, the official system estimated around 550,000 people came to the UK.

The authors warn that Brexit could lead to a surge of illegal immigrants unless the Government does more to tackle the issue.

“Without effective enforcement of immigration laws and regulations, the result of Brexit won’t be that we “take back control” of our borders, as the prime minster has promised. It will be a surge in illegal immigration”, the report said.

Ministers must get better at deporting people who should not be living and working in the UK, they added.

Immigration Minister Brandon Lewis said: “Our laws are being enforced. In fact, it is harder than ever before for those with no right to be here to remain in the UK.

“We expect those with no basis of stay to leave voluntarily. Where they do not, we will enforce their removal. This includes foreign criminals of whom we returned more than 6,000 last year.

“At the same time, we are continuing to reform legal routes to the UK from outside Europe and will use the opportunity of leaving the EU to take control of immigration from within the EU too.”

Official statisticians have said it is impossible to accurately quantify the number of people in the country unlawfully.

In an estimate 12 years ago, a Home Office assessment put the total unauthorised migrant population living in the UK in 2001 at 430,000.

The main count used to track trends in regular immigration is net migration, which is based on a survey of passengers and measures the difference between the numbers arriving in and leaving the country for at least a year.

Net long-term international migration was running at an estimated 248,000 last year.

The report also raises questions about whether data collected at the border and from National Insurance registrations could shed more light on immigration estimates.

And it claims that the Government has great difficulty enforcing tough-sounding policies to tackle illegal immigration.

Dr David Green, director of Civitas, said: “In recent years, successive governments have shown all the signs of wanting to hide the true scale of immigration from members of the public.

“The Government has better calculations of the scale of both legal and illegal immigration but has deliberately suppressed publication.”