Millions of EU nationals can secure their right to stay in the UK after Brexit from Saturday as the Home Office fully launches its Settlement Scheme.

An expert said the department faces an “enormous” task, with more than three million people expected to be eligible to apply to carry on living and working in the country.

Some 200,000 have already secured their status during private and public test phases.

From Saturday, the EU settlement scheme will be open to citizens of Iceland, Liechtenstein and Norway, which are in the European Economic Area (EEA) but not EU member states, as well as those from Switzerland.

Following the full launch, applicants can use a wider range of documents as proof of their identity and nationality, while those who do not wish to, or cannot, use a mobile phone ID verification app will be able to send in a passport or other document by post.

Madeleine Sumption, director of the Migration Observatory at the University of Oxford, said: “The task that lies ahead is enormous.

“Over the next couple of years the Government will have to document around 3.5 million EU citizens and their family members – several thousand people per day.

“In the large majority of cases, this will be a simple and easy process, both for the applicants and the Government.

“But there will also be challenges. Some EU citizens may find it difficult to apply and others simply won’t realise that they have to.”

She said the Windrush scandal showed how confusion around legal status can lead to “big problems”, adding: “Even with a well-designed, simple application and a large communications campaign, if the Government wants to get close to 100% coverage, it has a major challenge lying ahead.”

Immigration Minister Caroline Nokes said: “I am incredibly proud that our free EU Settlement Scheme launches today because it means that millions of EU citizens living in the UK, who are our friends, family and have made this country their home, can stay regardless of the UK’s relationship with the EU.

“More than 200,000 EU citizens have applied during the test phases of the scheme, including 8,000 on the first day of the public test phase.

“My message to all EU citizens is that this is a simple and straightforward process and some of the personal experiences I’ve heard have been from EU citizens who received status in a matter of hours.”

Successful applicants to the scheme are granted immigration status confirming their right to continue living and working in the UK indefinitely.

EU nationals and their family members who have lived continuously in the country for five years can obtain settled status.

Those with less than five years’ residence can acquire pre-settled status, which can later be converted into settled status.

The deadline for applying will be June 30 2021 in a deal departure, or December 31 2020 if the UK leaves without a deal.

The Government has designed an online application platform from scratch.

Applicants are asked to prove their identity, declare any criminal convictions and upload a facial photograph.

Officials check employment and benefits data to confirm residence and all applications are run through UK criminality and security databases.

Government estimates indicate that between 3.5 million and 4 million EEA citizens will be eligible to apply.

The Home Office has assigned more than 1,500 operational staff to the scheme, and earlier this week rolled out a nationwide advertising campaign ahead of the launch.

Up to £9 million of funding is available for voluntary and community sector organisations so they can help vulnerable people apply.