The proportion of EU citizens being granted a temporary, more precarious “pre-settled status” in the UK has continued to rise, the latest Home Office statistics show, and the backlog of unresolved cases has grown to more than half a million, causing unease among campaign groups that support EU nationals living in Britain.

Most of the estimated 3.4 million EU citizens resident in the UK must apply for settled status if they want to continue living here legally after Brexit. The latest EU settlement scheme statistics show that 590,300 people applied for settled status in October, bringing the total number of applications to 2,450,000.

Just over 1.9 million people have been granted some form of status in the UK. However, the proportion of people being allocated the more precarious, temporary pre-settled status continues to rise, jumping from 32% in the testing phase of the scheme to 34% in the month after the national launch in March, and up to 44% of all applications processed in October.

EU campaigners said it was positive to see more than half a million people applying for the status for the second month running, but expressed concern at the rise in the number of applications which have not yet been approved, with a backlog now of more than 525,200.

Nicolas Hatton, a co-founder of the EU citizens’ campaign group the3million, said it was hard to understand exactly why the backlog was growing. “We don’t know the reason. They may have processed the easier cases at the beginning, and the more difficult ones are creating a backlog. But more people are waiting now,” he said.

The group described the rise in the proportion of applicants getting the “inferior pre-settled status”, which represents a limited leave to remain in the UK, as a worrying trend. Although many applicants will have been correctly granted this status because they have not yet been in the country for five years, some are accepting this outcome because they have struggled to provide evidence that they have already lived here for that period. People who are granted pre-settled status will have to reapply for the full, permanent settled status once they are able to provide evidence that they have lived continuously in the UK for five years.

Elena Remigi, the founder and director of the In Limbo project, which represents EU citizens, said: “The statistics show a growing number of people applying for the settlement scheme, but we’ve also noticed an equally growing number of people waiting for several weeks, if not months, before receiving a reply. The elderly in particular seem to be the ones struggling with this scheme and many are told to provide further evidence. Many are receiving pre- rather than full settled status.”

Stephanie Dawoud, of the immigration organisation IMIX, said: “While the Home Office is doing comparatively well in terms of processing the number of applications, we still don’t have any robust numbers of EU citizens and their family members in the UK, which the statistics can be measured against.”

The Home Office said EU citizens and their families have until 31 December 2020 to apply, and added that applicants can apply for an administrative review if they think they were wrongly granted pre-settled status.