THE number of illegal migrants in Britain is still unknown because ministers do not have the basic data to track who is here, experts warn.
Officials also have no grip on how many use the European Convention on Human Rights to dodge removal, the Migration Observatory at the University of Oxford says.
Its report reveals the Home Office does not record how many apply for, or are granted, human-rights-based permission to remain.
It also warns huge gaps leave it unclear about the effects on public services, local areas and crime.
Director Dr Madeleine Sumption said: “UK membership of ECHR is a major issue in public debate.
“This is in large part due to its impacts on migration policy.
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“But the current data can’t give us a clear picture of where and when it has most impact.
“This makes it harder for the public or policymakers to make an informed choice about an important decision with long-term repercussions for the UK.”
The University of Oxford experts say new pilots linking Home Office and HMRC data show promise, but warn the system still has a long way to go.
The Home Office said it inherited a migration system “out of control”.
