A motorcycle rider out on a shopping trip was arrested and detained for a month as part of a high-profile government crackdown on undocumented migrants working for food delivery apps.

Fernando Fontoura, 33, who moved from Portugal to the UK when he was 12, was arrested by immigration enforcement officers after he parked his motorbike near a grocery store in south-east London on 22 July. He was taken to a detention centre near Gatwick airport where he was held for 29 days.

“I’ve been here [in the UK] for 21 years. It is completely unfair,” he said. “[The Home Office] says I have no lawful basis to be in the UK. But my family is here. My fiancee is here. I’ve been paying taxes here for over 10 years. I studied here. I did my GCSEs and NVQs here. I received my insurance number at the age of 16.”

Fontoura’s parents moved to London in 2004. His father worked in construction and his mother worked as a cleaner. “I made my life here,” Fontoura said. “I grew up in England. I picked up the language, the culture and everything else. I integrated into the community and I’ve been here ever since, apart from a few years travelling.”

The Home Office has stepped up sweeps of workplaces looking for undocumented migrant workers since Labour came to power. Immigration enforcement raids targeting migrant workers and arrests for “illegal working” increased by about 50% in the first 10 months of the Labour government compared with the same period the year before, under the Conservatives.

The policy, which has been criticised by refugee charities, is a key part of the government’s faltering strategy to hold back the advance of Reform UK. The prime minister posted twice on X in August about arrests of hundreds of delivery drivers “cheating our system” and “working illegally”.

The Home Office opposed bail for Fontoura, arguing there was no evidence to support his claim that he entered the UK in 2004 with his family. But the Guardian has seen official documents demonstrating Fontoura grew up in the UK, including a letter from his secondary school in Stockwell, south London, which he attended from 2005 to 2008.

Other documents show HMRC issued him with a national insurance number in 2009, and he worked in an electronics store in Croydon in 2015. A 2006 Department for Work and Pensions document states his father came to the UK with his wife and children, including Fontoura, in 2004.

Fontoura was granted bail on 19 August. He has been banned from working and has to report to an immigration centre every fortnight while the Home Office investigates. “They allowed me out, but they cancelled my insurance number, so I’m not allowed to look for work or to do anything to maintain myself,” he said.

He lives with the constant fear of arrest. “They can take me back to [the immigration detention centre] at any time. Even though I’m outside, I’m not free. It makes you feel paranoid, because you know at any time you go back to the same nightmare that you’ve been dealing with for the last month.”

The Work Rights Centre, a charity supporting migrant workers, is helping Fontoura apply for settled status. He thought he was classed as a UK resident as he was able to come and go from the UK while travelling around Europe. He did not realise he needed to apply under the post-Brexit scheme for EU nationals.

Luke Piper, who is the centre’s head of immigration, said Fontura had a good case for settled status as people can still apply if they can demonstrate reasonable grounds for a delay.

He said he was concerned that the government’s crackdown on “illegal working” may be catching people who have legitimate reasons to be in the UK and people who are struggling to prove their immigration status.

“It is the draconian reaction [of the Home Office] to these kinds of issues that then produces dangerous outcomes, where people lose their job, end up detained, lose their house and so on,” Piper said.

The Home Office said it would not be appropriate to comment on a case that is still under investigation.