European Union citizens who want to remain living in the UK must apply to do so by midnight. 

From July 1, unregistered EU citizens will lose their legal status in the UK, meaning they cannot work or study. They could even be at risk of deportation. 

Before the UK left the EU, citizens from across the bloc could live, work and study in the UK without a visa – and UK citizens could do the same in EU states. It's called "freedom of movement" and is one of the key pillars to the EU's single market. 

But since the UK confirmed it would leave the bloc, EU citizens have been told to register for "settled status" to remain in the country. But advocacy groups say thousands of Europeans are struggling to apply, or even convince elderly relatives they need to fill in the forms.

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Italian citizen Claudia Giacomardo and her family are among those scrambling to meet the deadline. 

Giacomardo has already applied and been accepted for the post-Brexit "status." But her husband's application was rejected and they must now reapply. She also didn't realize her two children need to apply – so she must now send in their applications as well. 

"It's very stressful because we have two kids and I only applied for myself," Claudia told CGTN Europe.

The Giacomardo family went to the Italian Advice Centre (INCA) in north London for help.

INCA said the majority of its work is helping elderly people prove how long they've been in the UK. The rules state EU citizens must have lived at least five years in the UK to be immediately accepted, but anyone who has spent less time there may be granted "pre-settled status," which will allow them to gain full rights as soon as they pass the five-year mark. 

"In most cases, elderly people who've been here 50 years aren't in the system and that's where it becomes tricky," case worker Dimitri Scarlato said. "First they get anxious and annoyed and say 'I've been here for 50 years, why do I need to prove it?'"

"In some cases it's difficult, especially for women, because the bills are in the husband's name, so we have to find a creative solution," Scarlato explained. 

More than 5 million European Union citizens have applied to stay in the UK under its post-Brexit rules. But in the week before Wednesday's deadline, the government said it had been inundated with as many as 10,000 applications per day.

The government said its system is "slick and effective" and added the option to apply for a 28-day extension to submit an application. Immigration Minister Kevin Foster said the government will take a "flexible and pragmatic approach" to enforcing the rules for anyone who fails to apply in time, with some exceptions to be made for those who don't make the deadline.

"Our first reaction [to those who fail to apply] will be to give them 28 days notice to make a late application, rather than proceed to enforcement action," Foster told AFP. "What I'd say to anyone who is yet to apply is 'you've got until midnight on June 30 to get your application in. Don't delay, do it now.'"

UK Business Minister Anne-Marie Trevelyan told of her own mother's experience with the system. "It's been a phenomenal scheme. My mother, who is French but has lived in the UK for most of her life, applied and it was a very efficient process for her to do," she said.

Video editor: Nuno Fernandes