18/06/2014 08:15 BST | Updated 18/08/2014 06:59 BST

Migration Figures Could Be Wrong By 50,000 - It's Time to Reintroduce Exit Checks

According to a parliamentary answer I received today, the net number of people entering the UK last year could be 49,000 higher than official estimates.

In reply to a question I asked about the accuracy of the migration figures from the International Passenger Survey (IPS), the Director General of the Office of National Statistics wrote:

The latest IPS estimate for long-term immigration for the year ending December 2013 was 485,000, with a margin of error of +/- 29,000. The latest IPS estimate for long-term emigration for the year ending December 2013 was 295,000, with a margin of error of +/- 19,000.

Therefore there may now be almost 50,000 more people in Britain than expected or conversely 50,000 less. Taken alone that might seem low, but over the period of a five-year parliamentary term our estimates could be out by as much as a quarter of a million - roughly the population of Luton.

The ONS is not to blame; they do keen and careful work with the information they are given. They're simply not given enough of it. They calculate net migration figures using the results of the International Passenger Survey (IPS), a questionnaire taken by a random sample of travellers every year. In this survey, passengers are asked whether they plan to stay in the UK for the long term.

But even if accurate answers are given, only 5,000 migrants a year actually take the survey according to the Public Administration Select Committee. Using it as the foundation on which we build our migration estimates and policies is unwise.

We need the evidence to develop effective immigration policy

Immigration is a difficult and contentious issue which is changing the face of modern politics. To write a sound, fair and effective UK immigration policy we must have better statistics; anything less is cavalier.

Our immigration policy has to do two things simultaneously: First, we must come down hard on benefit and health tourism - something the Home Secretary has made substantial progress on. Secondly, we must welcome foreign investors, tourists, students and highly-skilled people who contribute a huge amount to the UK and its economy, before the majority return to their home countries. This is a careful balancing act that can only be achieved on a foundation of accurate data.

We must have a fuller statistical picture including information about the different categories of migrants - students, tourists, migrant workers, investors, asylum seekers and illegal immigrants - because each group requires different treatment. With this data we could detect trends, and see where to focus our policy efforts. Without it, we are left adrift and open to wild assertions and unsubstantiated fears from all quarters.

As I have said before, how can we plan for the future of schools and hospitals if we don't know how many people might need to use them? Before we can judge where to spend or invest taxpayers' money, we need to know where people are living, how long they might live there and whether it's affordable.

Right now we just don't have the proper evidence required to make these policy judgements and we don't have the data to plan for the future.

We must have proper exit controls

That is why, today, I'm again urging the Home Secretary to restore universal entry and exit checks to count people in and out of the country. These were recklessly abolished by the Labour government in 1998 which claimed they were an "an inefficient use of resources". This statement could not have been any less accurate.

So I'm encouraged by the Home Secretary's recent commitment to restore universal exit checks by the end of this parliamentary term. These new exit checks must go hand-in-hand with more thorough data collection. They cannot be a 'rubberstamping' exercise. They must allow us to properly monitor UK migration and respond appropriately.

Time and time again, the public has stressed to the political establishment that immigration is an issue that must be taken seriously. We can only claim to take it seriously when we collect proper migration data in earnest. People on all sides of the debate can agree that Britain and its people deserve better migration data.