The number of EU citizens and their families applying for UK residency after Brexit has hit 2m, following a record number of submissions last month that created a large backlog.

In September 520,600 people applied to the settled status scheme, compared to a previous high of 389,000 in April. There are an estimated 3.6m European citizens and family members living in the UK.

Priti Patel, home secretary, said she was "thrilled" with the surge in applications; the total includes 1.8m applications by the end of September and 200,000 so far this month.

But only 373,000 applications were concluded in September, creating a backlog of more than 147,000. Maike Bohn, a spokesperson for EU citizens rights group the3million, described it as "worrying".

"This indicates cases are becoming more complex and people might have more and more difficulties evidencing their residence in the UK," she said, adding that the3million regularly spoke to people waiting weeks or even months for confirmation of their status while they submitted further documentation.

The Home Office states that the average processing time for an application is five days, but has said this could be longer if people need to send further paperwork. Available support for applicants includes a helpline, toolkit and funding for community organisations, and an average of 20,000 applications are processed each day.

"There is plenty of support and information on offer to help people apply and get the status they need," said Brandon Lewis, security minister and deputy for EU exit and no deal preparations.

Anxiety among EU citizens remains high, however. Ms Bohn said the jump in September applications was because EU citizens were "terrified of the consequences of [a] no deal" departure on October 31.

EU citizens and their families have until at least December 2020 to apply for settled status. Until then the Home Office has guaranteed that they will be able to continue to live and work in the UK, under interim measures in place even if the UK leaves the EU without a deal on October 31.

Ms Patel cast doubt on these assurances in August when she announced that freedom of movement would end abruptly on October 31. Although she quickly backtracked on the plan, Ms Bohn said trust in the government remains low and EU citizens fear being exposed to immigration controls.

She also expressed concern about the large number of people granted pre-settled status, a less secure status which means the holder has residence for five years, but must update it at a later date. Some 43 per cent of concluded applications were granted pre-settled status last month, the same as in August.