In early May, Doris Ratnam sat at her kitchen table, trying to scan her German passport with her mobile phone. She was applying for “settled status” in the UK, the new immigration status most of the 3.4 million or so EU nationals living in Britain need to acquire if they want to stay in the country legally after Brexit. Ratnam, who is 72 and has lived in London since arriving as an au pair in 1968, was annoyed that she felt obliged to apply under the scheme to remain more securely in a country she considers her home.

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She was flustered by the process of attempting to get her phone to suck all her personal details out of her passport. Something was not working, and we sat for 20 minutes in near silence as she moved the phone slowly over the cover of the passport, as shown in a reassuring Home Office Youtube video, trying to get it to read the chip hidden inside the document. “Move the phone to read the chip,” Ratnam muttered, studying the guidance notes. “What am I supposed to do? Move the phone to find the chip. I feel stressed … it’s the technology.”

After repeated failed attempts, the app informed her she had been locked out of the system for 24 hours. It would take two-and-a-half months, two visits to the local town hall (an hour on two buses each way), a £15 appointment fee and numerous calls to a Home Office helpline before her status was approved. The process was dispiriting. “I shouldn’t be made to feel like a foreigner again after such a long time here,” she said.

Before the end of June 2021, if Britain leaves the EU with a deal, or by 31 December 2020 with no deal, most EU nationals resident in the UK must have applied for settled status if they want to continue living and working here. The EU settled status scheme is designed to fulfil the government’s promise that all EU citizens, their family members, and dependants living here before Brexit, will be entitled to remain, with no diminishment of their rights. Anyone who has lived here continuously for five years should, in theory, be able to get settled status easily; people who have been here for less than five years will be granted “pre-settled” status, requiring them to reapply for permanent status once they have racked up enough years of continuous residence (which means not leaving the country for more than six months a year).

For Europeans in the UK, the Home Office’s “EU Exit: ID Document Check” app is the gateway between belonging and exclusion. How well this piece of software works will be a crucial factor in the government’s attempts to present Brexit as a success. In the past year, almost 1.5 million Europeans living in the UK have grappled with the Home Office application process and managed to secure settled or pre-settled status. The Home Office would like us to celebrate this as a bureaucratic success story, and in a very optimistic frame of mind, perhaps we might.

The government has allocated about £460m to the scheme, of which about £50m was spent on developing this unflashy app, its opening pages headed with the outline of a crown on a royal blue background. At the launch of the scheme in March, a Home Office radio advertising campaign reassured people: “It is free, and all you need is your passport or ID card and to complete an online form.”

Former home secretary Amber Rudd was cheerfully optimistic, promising (in an aside that revealed more about her wardrobe choices than about Home Office reliability) that the digital application process would be as easy to use as setting up an online account at the fashion chain LK Bennett. Home Office figures state that 75% of applicants are completing the identity check “app journey in under eight minutes”.

In May, I was taken on a tour of the Home Office’s Liverpool offices, where 1,500 workers were then handling about 6,000 “settled status” applications a day (it has since risen to 20,000). At the end of the tour, one of the senior civil servants in charge of the scheme said it would be good to see media coverage emphasising how well things are working. “In an ideal world, we want you to write an article saying you have come here, and there’s nothing to be afraid of.”

But what is at stake here is so enormous, and the potential for things to go wrong so real, that it is hard to be sure whether people should be feeling confident or apprehensive. Even if the application process achieves an improbably hopeful 95% success rate, it could still have disastrous consequences for those left out – who could number more than 150,000. (And it is improbable: a report last year found that take-up rates for similar large-population registrations ranged from 43% in the US to 77% in Spain; the only scheme that came close to a 100% take up was an ID card system in India, but this was after almost £1bn was spent on raising awareness.)

After the deadline, those who have failed to apply will gradually be transformed from legal residents into undocumented migrants. In the hostile environment – the obstructive and unwelcoming bureaucratic culture promoted by Theresa May when she was home secretary – they will be unable to work, rent somewhere to live, access free healthcare, drive, open a bank account, get a mobile phone contract or travel without being asked to prove their status. They will gradually discover that normal life has become impossible.

The Home Office has never attempted a digital exercise on this scale. All the unknowns – numbers, timing, terms of the deal – have presented developers with unexpected challenges. By the end of January, two months before it was due to launch nationally, IT specialists working for the Home Office had successfully designed a scheme that charged applicants £65. Days before the app was rolled out for public testing, they were told that the fees were too politically sensitive and needed to be scrapped – leaving them no time to rebuild the app without the fee pages. So, as an awkward last-minute fix, initial applicants were charged anyway and had to get their money refunded later. The decision to scrap the fee also meant the government instantly lost about £190m of revenue that the scheme was meant to bring in.

“They were trying to deliver the biggest, most contentious new system that any of them had likely ever worked on, while the basic requirements were changing around them, even days before they went live,” said Joe Owen, the programme director of the Institute for Government, a thinktank working to make government more effective. Owen has been tracing the development of the scheme since the EU referendum.

One major problem was that the scheme does not yet work on the iPhone. The Home Office has been struggling with Apple’s refusal to allow third-party developers to use its contactless system since the start of the app’s development. Given that iPhones account for almost half the smartphones in the UK, this creates a major headache for applicants. Many people have had to borrow phones, or take the longer route of sending off their passports for manual scanning. Officials say the app should begin to be available on iPhones later this month.

Another complication is that it is not known how many EU nationals there are in the UK. The figure of 3.4 million that the government is basing all its plans on is thought by many to be an underestimate.

Facebook Twitter Pinterest EU citizens in London lobbying MPs to guarantee their post-Brexit rights. Photograph: Stefan Rousseau/PA

“Nobody knows exactly how many are eligible,” said Madeleine Sumption, director of the Migration Observatory at the University of Oxford. The government’s estimate was “almost certain to be too low because it doesn’t include people living in non-private addresses like hostels or care homes, and the figures are thought to undercount several groups – new arrivals, EU/non-EU dual citizens, and people who spend part of the year outside the UK.”

Nor does the estimate include close family members from non-EU countries, who are also eligible under this scheme. The total number of people who need to apply could perhaps be as high as 4 million.

For the moment the political rhetoric remains warm, and officials say people who have a good reason for missing the deadline will be allowed a “reasonable” further period to apply, but the small print spells out the chilling consequences of failing to get status. Although politicians are not currently choosing to highlight this publicly, the Home Office has made it clear in planning documents that, from January 2021 (in a no-deal scenario), anyone without valid UK immigration status “will be liable to enforcement action, detention and removal as an immigration offender”.

It is not surprising that so many of the 3 million-plus are feeling vulnerable and furious. They were demonised by the leave campaign as the problem to which Brexit was the solution; they have faced years of hostile newspaper headlines; they are angry that the scheme has been developed as an application process rather than a registration scheme (meaning that the status is only acquired by successfully applying for it; under a registration scheme, EU citizens who had failed to apply successfully for the status would not immediately become illegal). They point out that this is not the automatic guarantee of rights the Vote Leave campaign and the government promised. Being forced to apply for the right to stay in their homes has been the final insult. For all its royal blue neutrality, many see the app as performing a distasteful political function – locating them, counting them and classifying them.

Meanwhile, all over Europe, about 1.4 million expatriate Britons are anxiously monitoring the scheme, aware that their own treatment could depend largely on how generously the UK government treats EU citizens.

In April 2018, it emerged that thousands of people who had been born in Commonwealth countries and moved to the UK as children in the 1960s and 70s, when there was free movement between Britain and its former colonies, had become the victims of changes to immigration legislation. In what became known as the Windrush scandal, those who had never applied for British passports found themselves wrongly classified as immigration offenders. Some were detained and removed from the UK, back to countries they had not visited in half a century. Others lost their jobs or homes or were denied NHS treatment.

Their experiences have alarmed EU nationals. The scandal highlighted how poor the Home Office’s capacity is for accurately identifying who is living in the UK legally or illegally, and its reputation has crystallised as an institution that combines malice with incompetence. Many of those obliged to apply for the scheme find the prospect of giving all their personal details to the Home Office disturbing.

For about a quarter of applicants, the process is more complicated than simply submitting passport details and completing an online form. The Advertising Standards Authority has recently ruled that the reassuring Home Office radio advertisement must not be broadcast again, after a complainant pointed out that in some cases applicants had to provide much more documentation than just a passport or ID card.

Since the beginning of the year, Labour has been warning of looming problems with the system, even talking of “Windrush on steroids”. But such warnings are often firmly slapped down as just being part of “project fear”. (“I find your comparisons to Windrush inappropriate,” Priti Patel, the home secretary, told the mayor of London, Sadiq Khan, this month.)

There is already concern from immigration lawyers about the upbeat slanting of statistics. The Home Office likes to say that almost 1.5 million people have been granted “some form of status”, but this masks the fact that currently about 40% are getting the inferior pre-settled status, which obliges them to adhere to strict rules on continuous residence for up to a further five years or risk getting pushed out of the system.

Even the Conservative and arch Brexiter MEP Daniel Hannan has voiced concern on Twitter, warning that he has had cases of EU nationals in his south-east England constituency being denied settled status despite living in the UK for years. “This is a breach of the assurances I and others gave during the referendum.” He called on Patel “to sort this out … before we end up with another Windrush scandal”.

Nicolas Hatton, co-founder of the3million, an organisation set up to support EU nationals, describes the decision to introduce an application system with a cut-off date as a timebomb, because so many will fail to apply on time. Switching metaphors, he warns this will be an “illegal immigrants factory … designed to create thousands and thousands of illegal immigrants”.

At the Home Office building in Liverpool, where many of the 1,500 people employed to process the applications are based, there is a relentlessly positive atmosphere. Everyone here is aware of the damage done to the Home Office’s reputation by Windrush. In recent years, the Home Office has been condemned by politicians for being steeped in a “culture of disbelief”, where staff are expected to probe for tiny inconsistencies in the accounts of refugees, and where officials are instructed to “deport first, hear appeals later”.

Many Windrush victims described how they had tried repeatedly to explain that they were not illegal immigrants, but had been ignored, or simply unable to find a Home Office caseworker ready to listen. Before she resigned, Amber Rudd apologised for the “appalling” actions of her own department, blaming a culture in the Home Office which had “lost sight of individuals” and become “too concerned with policy”. In turn, her successor Sajid Javid promised to introduce a “fairer, more compassionate” immigration system. This hasn’t materialised in most of the department, according to immigration lawyers and caseworkers, but in these open-plan offices in Liverpool, up an escalator, above a Tesco and a florist, something does appear to have changed.

Officials are working to instil a new, friendlier ethos within the department dealing with EU nationals. Drawings of cups of tea (with the teabags still in) have been chosen for the branding of the Home Office campaign, to evoke a friendly message of welcome. “We are absolutely, and I can’t stress this enough, not trying to say no,” one of the senior civil servants (who asked not to be named) said. “This is about trying to grant the right. This is not about trying to trip people up. This [application] is something people don’t want to do, and we get that, but we’ve set this up from scratch. All this is here to try to say yes to European citizens, to try to give them their rights.”

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If things are working, the full application should take about 15 minutes (there are a few more questions on residency and criminality once ID checks are completed). Under the new scheme, the Home Office doesn’t care if applicants are self-sufficient, studying or working – simply whether they are resident in the UK or not; this is verified by making instant checks with HMRC. Applicants have to do three things: prove their identity, show that they live in the UK and declare any criminal convictions. Once data has been scanned from people’s passports via their phone, they have to take a selfie, so the app can identify if the correct person is applying. The app checks identity through facial matching in the same way travellers are checked in airports at e-passport gates.

To reduce the possibility of fraud, there is no physical document at the end of the process, just a digital record, which can be shared with a landlord or an employer (after Brexit, they will have to check EU nationals’ eligibility) via a time-limited unique code, on a smartphone.

On one floor in Liverpool, staff sit at computers flicking through screens. A passport photograph flashes up, and the employee checks to make sure it matches the selfie taken and submitted through the app. Although much of the system is automated, every case is checked by a human before a decision is made. These human checks can take just 10 minutes. Some people are getting an email back telling them they have settled status within a couple of hours.

When I visited, there was a homely smell of microwaved stew; helium balloons hovered over the desk of someone who had been given a baby shower. Special EU Settlement Resolution Centre teacups have been printed for staff, with inspirational slogans on them. Most of the staff are newly hired, many of them students. One of the few longer-serving members of staff, who has worked at the Home Office for five years, said it was a relief not to have to be so sceptical when dealing with people’s applications. “Before the onus was more on ‘prove it’. Now we are doing everything we can to help,” she said. “When I first joined, it was noticeable that not many cases would result in us issuing the applicant with what they needed.”

The only people likely to be refused will be those with “persistent and serious” criminal records and, so far, only one person has been refused – although a number of people have been dismayed to get the lesser, more precarious pre-settled status, despite having been in the UK for more than five years. Campaigners suspect that the difficult cases may be going to the bottom of the pile, to keep the figures looking favourable.

When the project began, one of the senior civil servants in charge ordered a number of copies of a book called In Limbo, compiled by an Italian translator Elena Remigi, so he and colleagues could read the 144 testimonies of EU nationals resident in Britain, people who were worried about their post-Brexit future here, people who are, the blurb says, “haunted by the poignant question: where is home?” They say the book helped them understand the worries faced by those being asked to apply. Videos have been made for people who struggle with literacy, there is helpline assistance for those who are not confident with technology. The guidance has been translated into all 26 languages (although the helpline advice is only available in English and Welsh). In addition, £9m has been allocated to funding charities (organisations such as Citizens Advice and the East European Resource Centre) to help an estimated 200,000 vulnerable or hard to reach people to apply. Downstairs there is a hotline; this is the first time in 10 years that people have been able to call a Home Office number and speak to a caseworker, rather than an employee at an outsourced firm, reading from a script.

In August, Patel announced an end to freedom of movement in a no-deal scenario at the end of next month. Officials quickly had to clarify on her behalf that free movement would not be ending on that date (since EU law continues to apply until its legal foundation is repealed). Unfortunately, the home secretary’s premature announcement led to a spike in calls leading to long waiting times.

“We’re trying to change the perception of the Home Office,” the woman who heads the call centre said. Staff have dealt with a lot of people who were “upset, frightened and angry”, she said. “We understand why. This is something that has happened to those people. They weren’t consulted or even given a vote in it. They are now having to apply for something that they always had.”

Windrush victims waited years for anyone to pay attention to their difficulties with the Home Office, as they lost jobs and homes and faced detention. By comparison, a mildly famous French baker or Polish chef struggling with the EU status app need only send an irritated Tweet for newspapers to print outraged articles. The reality TV celebrity Fred Sirieix, after tweeting his frustration, had calls from the Home Office within 24 hours to resolve things. Home Office staff seem at pains to act fast to resolve high-profile cases, to quell the noise; but less clear is what happens to those who have less of a public profile.

For some people, the experience is genuinely easy. Some people describe doing it while sitting on the sofa at home, and being pleasantly surprised at getting an email confirming that they have been granted settled status within hours. The difficulty is that while around three-quarters are getting through easily and a quarter need to submit further information, a small proportion will have more complicated experiences.

We already know that too many people are wrongly being allocated pre-settled status instead of the more permanent settled status, a problem that came up during the testing phase, Home Office staff told me. “One of the things we were surprised about in early testing was that people thought they were clicking the button for full settled status, but they were actually accepting pre-settled status, and then being surprised. So we tried to make quite a lot of changes to the guidance to reinforce that,” an official said.

But the problem persists, and campaigners say there are still oddities in the design of the application form, which does not ask people how long they have lived in the UK or which status they hope to get. Only the most well-informed applicants will know they can challenge an incorrect allocation of pre-settled status.

Facebook Twitter Pinterest Home secretary Priti Patel speaking at the Conservative party conference in Manchester earlier this month. Photograph: Danny Lawson/PA

The immigration lawyer Chris Desira has spoken to audiences of EU nationals at more than 200 information sessions arranged by embassies and community groups all over the UK in the past three years. He has identified many vulnerable groups who might find it hard to supply the evidence required to prove that they qualify for settled status – elderly people, people with disabilities, children in care, stay-at-home women who haven’t worked or paid bills, and victims of domestic abuse whose partners have all their papers. He is conscious that the awareness of the need to apply has not got through to everyone. “I am massively worried, massively,” said Desira.

He has seen older people who have been here for decades crying in meetings, worried they are going to be put on a plane out of the country. “Even when you tell them, ‘I am confident that if you fill in this form, you will be fine, you will get settled status’, the anxiety and the stress and everything that is happening around them prevents them from hearing that message.”

His concerns are echoed by Chai Patel of the Joint Council for the Welfare of Immigrants, who warns that the scheme is set up to be easy for people who are “wealthy, well-educated people”. He is concerned at the absence of a physical document proving status. “The scheme is very easy if you know your rights, you’re online and you’re bolshie enough to be able to stand up for what you’re entitled to. It won’t work so well for the more vulnerable. We are expecting hundreds of thousands of people to be left without status if the scheme continues as it is,” he said.

I met Chris Desira at an event organised in a central London YMCA hall by the German embassy earlier this year, where he and two German diplomats, attempted to answer the questions of people confused by what they needed to do in order to ensure they could continue to live in the UK. While the official line appeared to be “Don’t panic”, the cumulative effect of almost two hours of anxious questions left many feeling disturbed.

One by one, German citizens stood up to voice their alarm. “It’s giving me stomach ache. I’ve been here since 1961,” one woman said, before being reassured that she simply needed to make the application, and she would be fine. (Stephanie Dawoud of the immigration charity Imix, who was translating into my ear, said most of the meetings she had attended had a similar feeling of distress, particularly among older people, who were particularly worried by the unfamiliar notion of apps and applying digitally.) A woman in her 30s was worried about whether she should transfer her business out of the country.

The German diplomat presiding over the occasion (who asked not to be named) exhibited a mournful sense of humour at some of the questions.

“What happens to German civil servants?” someone asked.

“I would love to know that, too!” the diplomat replied.

“Can I come into the country after Brexit?” one woman asked.

“Yes, unless you scare the people are the border into thinking you are a threat to national security,” said the diplomat.

“Should I stockpile food?” another wanted to know, to wry laughter from the room.

“The exciting thing is that you’re jumping into a big black hole,” the diplomat replied.

There were questions about eligibility to healthcare in a no-deal scenario, questions about how to apply for dual nationality and questions about how UK pensions would be uprated if they were paid in Germany. “I have no information whatsoever on how it will pan out. You don’t know what the British government will do,” the diplomat said sadly.

Doris Ratnam was at the back of the room, wondering how she was going to organise herself to apply. She had left her small Black Forest village near Baden Baden in 1968, aged 20, hoping to learn English, a language that neither of her parents spoke. She married a Malaysian citizen in London; he became naturalised decades ago, but she didn’t want to, because for a long time it was difficult to get British citizenship without losing your German passport. (That changed in the pre-Brexit period.)

She felt disheartened at applying for a status she considered to be hers already, as well as alarmed by the digital application. She invited me to watch the process of using the app in May, at her neat north-west London home, reached through a garden of pink roses and trimmed hedges. “I’ve been paying taxes here for 50 years, it should be simple,” she said, offering me coffee and ginger snaps.

But her passport could not be read by the app, even though she had travelled through a passport e-gate, which uses the same technology, only four days earlier.

The process of applying had made her think about her attitudes to Britishness. “I find it difficult to know after all this time whether I feel at home here. I certainly don’t feel British, like a British person, but I have English friends … I feel in-between; I feel both. There’s a saying: the British are too polite to be honest, the Germans are too honest to be polite. I think there is something in it.”

On the helpline, after much time listening to jangly hold music, the Home Office helper was both polite and honest, but had no answer as to why the app was not reading the digital code. She was advised to seek out one of the 80 designated EU settlement scheme scanning offices (in council offices and town hall register offices) where the passport could be scanned manually.

It took weeks for Ratnam to get an appointment at Ealing town hall, but she finally went on 4 July, consulting a photocopied map to find room 1.13, winding right, then left along echoing corridors, then right, then left again, up some marble steps, past a bust of Chopin through the beautiful, almost empty mock-gothic building, soon to be decommissioned and turned into a boutique hotel. Once we arrived at a small, pink-doored room, the official inside was unable to help, also attempting to swipe the passport on a phone until the system locked her out, too. So Ratnam then sat in the waiting room on the phone to the resolution centre in Liverpool for another 40 minutes , asking for help. “I can only advise that the application is locked for 24 hours. We can’t override that,” an official said. “For the time being there is nothing further we can do to help.”

“I’m just fed up,” Ratnam said, a red flush of worry creeping up her neck. “I’m getting worked up; I can’t even get my words out. I don’t want to keep trying.”

She organised a second appointment at the town hall on 10 July. The passport was finally scanned, quite easily, that day, but two days later she received an email asking her to upload an image of her old passport showing a historic stamp giving her indefinite leave to remain. The same email told her that the Home Office could find no record of her indefinite leave to remain and wanted to “confirm that you are related to your EU family member as claimed”. The email was a mistake. She couldn’t work out how to upload the passport; there was another long phone call to Liverpool on 15 July, after which she managed to send off the picture.

“I can hear it in your voice, how anxious you are,” a call handler told her.

“Why can’t you just check my HMRC records?” Ratnam asked. “I’ve been paying tax for long enough.”

On 16 July, an email arrived telling her that her documents had been sent in an “unsupported format and we have been unable to attach the files to your application”. But puzzlingly, a minute later, a second email arrived, saying that her “application to the EU Settlement Scheme has been successful”.

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Ratnam has managed to secure her status. Nothing catastrophic went wrong with her application – just a series of irritations that sucked up her time and lowered her mood. Similar irritations will be felt by tens of thousands of others going through the process, reinforcing a sense of alienation. “I’m annoyed that I had to do it after 50 years here. There were mistakes and it was stressful. I don’t feel welcome having to go through a process like that. [See Footnote].

Campaigners worry most about those who do not realise they need to apply, or those who have difficulties converting their pre-settled status into the permanent settled status in the years that follow Brexit. Nicolas Hatton of the 3million charity warns: “On 1 January 2021, if there is no deal, and you haven’t applied, you will be an illegal immigrant. The hostile environment is no joke. That’s when the timebomb will explode.”

• This article was amended on 8 October 2019 to clarify that most but not all EU nationals resident in the UK must have applied for settled status if they want to continue living and working here. Details of the EU Settlement Scheme and who does and doesn’t have to apply are on the government website: https://www.gov.uk/settled-status-eu-citizens-families/eligibility

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