Gaps in Government data are making it difficult to know whether the EU Settlement Scheme is working, immigration experts have claimed.

EU citizens and their relatives are asked to apply to the Home Office’s EUSS scheme in order to carry on living and working in the UK after freedom of movement with the European Union ends.

But without “significant investments in new official data, there will be no way of verifying whether it is reaching this goal”, the Migration Observatory at the University of Oxford warned in a report.

So far more than 3.4 million (3,468,700) applications have been received for the scheme ahead of the June 2021 deadline.

The Government has invested a lot of effort in making the EU Settlement Scheme easy to use, but with any scheme of this size it is inevitable that some people will fall through the cracks

According to the latest figures, a decision has been made on more than 3.1 million applications (3,147,100), leaving a backlog of 321,600 still to complete.

Some 58% (1,813,300) of concluded applications were granted settled status – giving them permanent leave to remain living and working in the UK – while 41% (1,299,300) were given pre-settled status, where they would need to re-apply again after living in the country for five years to gain permanent residence.

There were 23,900 applications void or withdrawn, 10,000 classed as invalid and 600 refused – where someone is not eligible to apply or has failed to provide sufficient proof of residence.

The report said there were “significant gaps in the evidence base about the EUSS”, adding: “The inclusiveness and coverage of the scheme are crucially important, since the default policy position is that people who do not secure their status through EUSS will lose their legal status in the UK.”

Last month the Home Office warned applications to the scheme would be hit by delays due to the coronavirus outbreak.

The Observatory’s report warns this could cause problems with identifying vulnerable EU citizens who most likely to be among those who fail to apply and disrupt the collection of official data collection.

The latest figures show in the last month the number of applications being submitted and finalised have each dropped by more than 100,000.

There were 125,000 applications received in March and 148,800 concluded. In February there were 235,800 received and 268,100 completed.

These are the lowest monthly totals since June last year when 121,000 applications were recorded and a decision was made on 137,600.

Madeleine Sumption, director of the Observatory and author of the report, said: “The Government has invested a lot of effort in making the EU Settlement Scheme easy to use, but with any scheme of this size it is inevitable that some people will fall through the cracks.

“It will be very hard to know to what extent this has happened, without a parallel investment in new data.

“For a host of reasons, it’s possible that the number of EU citizens granted status through the scheme could greatly exceed the current official estimate of 3.4 million but that wouldn’t necessarily mean the task is finished.

“Any discussion about whether to extend or drop the deadline next year will have to take place without a clear picture of how many people have not yet applied.”

The report claims the official estimate of 3.4 million non-Irish EU citizens living in the UK is not a good guide to the number of people eligible to apply because the figure does not take into account those living in places like care homes or caravan parks but may still include those who have emigrated.

It said: “The actual figure could be considerably higher, but at this stage it is not possible to say by how much.

“This means that when the deadline for applications arrives, it may be impossible to know how many people are set to lose their legal status and become irregular migrants because they did not apply.”

A Home Office spokesman said: “We are working closely with employers, local authorities and charities to raise awareness of the EU Settlement Scheme and identify those who are eligible.

“A wide range of support has been available for applicants since the scheme opened, including throughout the coronavirus pandemic.”