Almost 600,000 EU nationals and their relatives have applied for post-Brexit residency rights in a single month, as the backlog of cases surges to more than 520,000 – as new figures show.

Government data shows 590,300 applications to the EU settlement scheme were made last month, compared to 520,600 in September – marking a 13 per cent increase.

Meanwhile 525,200 applicants are still waiting for an outcome on their application – more than a fifth of all applicants – fuelling fears that a backlog is building up ahead of Brexit.

In the previous month, 18 per cent – or 335,700 – of people who had applied were still waiting for a decision, indicating that the rate at which applications are being processed is slowing.

Stian Johansen, 29, has been waiting for more than two months for a decision on his application, despite the government saying the process should usually take one to four days.

The German national, who works for a tech company in London and has been living and working in the UK since 2013, told The Independent: “I’ve called them twice, both times they said there’s nothing to worry about but they were not able to give details.

“I’ve been here for more than five years and I gave them all the evidence they asked for, so it should be a pretty straightforward case. It’s creating a lot of uncertainty.”

The figures show there has also been a rise in the proportion of applicants granted only pre-settled status, which will require them to reapply for permanent status once they have been in Britain for five years, with the figure now standing at 45 per cent of all outcomes.

Campaigners said some of these people may have been wrongly denied permanent immigration status, particularly after a number of high-profile incidents of this kind emerged in the media.

Concern has also been raised about the cohort of EU nationals who may not be aware of the scheme, and therefore could be left undocumented and at the mercy of a “hostile environment” after Brexit.

Luke Piper, immigration solicitor at South West Law, said: “I regularly meet – and continue to do so – people who have no idea that they need to apply. No scheme is ever 100 per cent, those that don’t apply need good reasons for not doing so.

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“The whole scheme is set on a presumption everyone knows that they need to apply – in my experience this is a dangerous presumption.”

EU citizens have until at least December 2020 to apply under the settlement scheme and protect their rights in UK law.