Registering more than 3 million EU migrants already living in Britain would present the government with a huge administrative task, according to a new report.

Experts looked at the existing regime for applying for permanent residence to examine possible issues that could arise if any new system was introduced following the Brexit vote.

Their analysis suggests that if all the European Economic Area (EEA) citizens living in the UK at the beginning of 2016 applied for permanent residence in the same year, this would amount to the equivalent of around 140 years of work at recent rates of processing.

Britain is expected to seek to changes to free movement rules following the outcome of the referendum in June, but details of the system have yet to be outlined.

Madeleine Sumption, director of the Migration Observatory at the University of Oxford, said: “Depending on how long Brexit negotiations take, the government may need to register EU citizens already living here quite quickly.

“Given the sheer number of EU citizens who would need to register and the potential complexity of the process, this will be a formidable task.”

The observatory looked at the existing regime through which EU nationals apply for permanent residence. Under the rules, those who have lived continuously in the UK for at least five years automatically have a permanent right to reside.

The paper said that while the actual process in coming years may be “quite different”, examining the current process “gives an insight into the kind of issues that could arise as any future registration mechanism is implemented”.

Assuming free movement comes to an end after the exit process is formalised, EU citizens may need to obtain documents demonstrating their residence rights within a relatively short period of time in order to distinguish themselves from newly arriving EU citizens who do not continue to enjoy free movement rights, according to the study.

Sir Julian King has been tasked with improving security in Europe. Photograph: Foreign Office/EPA

Meanwhile, Britain’s new EU commissioner, Sir Julian King, has been asked to help develop European security and counter-terrorism plans. The diplomat will become commissioner for the security union, tasked with beefing up the EU’s counter-terrorism role and taking action to prevent radicalisation.

King, currently UK ambassador to France, was appointed by David Cameron in one of his final acts as prime minister, to ensure that the UK had a place around the table at the EU executive in Brussels. The vacancy arose after Jonathan Hill stood down as financial regulation commissioner following Britain’s vote to leave the EU.



The portfolio offered by the European commission is not the derisory job in charge of paperclips or EU language policy that some Brussels insiders had joked about, but King will be a junior member of the commission, outranked by existing politicians.



He will report to the commission first vice-president, Frans Timmermans, who will have the final say over any legislative initiatives. King will not attend ministerial meetings, usually a key part of a commissioner’s job. Dimitris Avramopoulos, the commissioner in charge of home affairs and migration, will represent the commission on security policy at meetings with EU ministers and in the European parliament, a decision already being seen as a snub to the UK.



The job underlines the EU’s hopes of maintaining strong ties with a post-Brexit UK in the fight against terrorism. The EU executive has been pushing for a more joined-up response to terrorism, even before the recent attacks in Paris, Brussels, Normandy and Nice.



Following the Brussels attacks in March, Jean-Claude Juncker, the president of the commission, said: “We need capital markets union, energy union, economic and monetary union, but we also think that we need a security union.”



Juncker interviewed King in July and then spent some time “meditating” on the decision, according to a spokeswoman.



If confirmed in post, King will get his feet under the table almost 18 months after the launch of the EU’s security strategy. The spokeswoman said he would have to deliver “very concrete anti-terrorism measures”, adding that “obviously fighting terrorism is primarily a member state’s responsibility”.

Timothy Kirkhope, a Conservative MEP, said the portfolio choice sent “a strong signal that the security relationship between Britain and the EU will remain of key importance post Brexit”.

In a letter to King, Juncker said the EU was going through one of the most testing periods in its history. He highlighted the problem of unemployment and the lingering effects of the financial crisis. “We have to cope with the refugee crisis, with the aftermath of the UK referendum and with the increased threat of terrorism,” he said.

No 10 welcomed the decision. “The UK will continue to fulfil our rights and obligations as a member state until we leave the EU, and the prime minister has been clear that we will be an active player, so it is right that we should continue to have a commissioner role,” a spokesperson said.

“Security is a vital issue for all member states and cooperation across the EU can help to better protect us all from the range of threats we face.

“The president called the prime minister [on Monday] evening to inform her of his decision. We now look forward to Sir Julian being confirmed in the role.”

King still has to be formally approved by all 28 EU member states. He will be questioned by MEPs at a hearing likely to take place in September. While the European parliament does not have a binding vote, Juncker has to “seriously consider” its views.

King can expect to be questioned about data protection, a topic that arouses strong passions in the parliament, which has a track record of voting down data collection schemes.

Rebecca Harms, a German MEP who co-chairs the Green group, said some British politicians “tended to be associated with mass data collection and closing borders”. “We need to agree our security strategy, but we have to do it with deeper cooperation and we have to be very specific about data collection,” she said.

She also voiced surprise that King was being offered “a key portfolio” rather than the “relatively unimportant job” expected. “This is not a portfolio that you give to someone who fills a gap between 2016 and 2018.”