Hundreds of British citizens with foreign-born partners who depend on an obscure legal loophole to allow them to live together in the UK could see their chances of family life made even tougher by the EU renegotiation, campaigners and lawyers have warned.

Current rules insist a British spouse must earn more than £18,600 for their loved one to be allowed to join them in the UK, regardless of the income of the foreign spouse or the family’s assets.

As a result, many have relied on a bizarre workaround known as the Surinder Singh route, in which a British citizen moves temporarily to another EU country with their foreign partner, before both enter the UK under EU freedom of movement laws.

However, the draft deal from the European commission, aimed at keeping Britain in the EU, includes a paragraph that seems intent on shutting down the loophole, agreeing “to exclude, from the scope of free movement rights, third-country nationals who had no prior lawful residence in a member state before marrying a union citizen or who marry a union citizen only after the union citizen has established residence in the host member state”.

The draft deal also says member states should be able to use the “abuse of free movement rights” as a reason to deny a visa, if the couple “had the purpose of evading the application of national immigration rules”.

Critics argue the current law on spousal visas penalises around 43% of the UK population, particularly mothers of young children, public sector workers and those living outside London and the south-east, who are more likely to be low paid. Families have challenged the Home Office over the minimum income rules, with the final appeal set to be heard at the supreme court on Monday.

Don Flynn, director of the Migrants’ Rights Network, estimates there may be about 100 families currently in the process of attempting the Surinder Singh route – although there is no official record – who will now have to apply for permanent status in whichever EU country they go to, before returning to Britain.

“The reality is that even when the income has been only just below the threshold, or if the British partner has a young child, or a foreign partner has a cast-iron guarantee of earning more, the Home Office has never once, in cases I’ve been aware of, exercised any discretion,” he said.

Sonel Mehta, founder of campaign group BritCits, which works with divided families and gives advice on the Surinder Singh route, said families felt they were again bearing the brunt of a government crackdown on immigration numbers, but had no one to lobby for them.

“People are panicking,” Mehta said of the draft deal. “It is yet another way to target families. And British citizens feel upset because this is driven by their own government. And this draft could close down another window when the door is already bolted shut.”

Couples who have attempted to use the loophole will have to leave any jobs or homes in Britain and set up home in another EU country, most usually Ireland, for at least three months, but more often six to 12 months. “We usually say to people the longer the better,” Mehta said. “We actually advise people to make as much of a go of it in that country as they can, to build a life.”

Danielle and her American husband, Michael, who met in California in 2008 and spent a few years living together in both the US and UK, were travelling in South America in 2012 when they found out the rules on minimum income had been brought in. Danielle had planned to return to the UK to train as a teacher.

For Danielle, this technicality, which hinges on EU freedom of movement rules, was the only way she could continue to live with her husband, despite the couple having been married for several years.

The couple had to give up plans to move to the UK and instead spent time working in Germany in order to then apply to bring Michael to the UK as the spouse of a EU citizen, exercising free movement rights, rather than comply with the British rule.

“It didn’t matter that we had been married and had already lived together for more than three years, including some of that time being in the UK,” Danielle told the Guardian. “There was no point even applying for a spouse visa as we couldn’t remotely meet the criteria.”

Danielle said she never considered spending time in the UK, away from Michael, to look for a job that would earn over the minimum as it would mean a separation of at least six months. “We got married because we wanted to be together,” she said. “It was a real challenge not succumbing to depression and anger. Why could I not do the simple thing that most couples take for granted – live together on the same patch of the Earth?”

The couple looked for jobs teaching English across the EU, with Danielle eventually finding a job in Germany, where she had spent part of her childhood. “I will be forever thankful to Germany for being so welcoming to us,” she said. “Every aspect of the German state that we interacted with was efficient and we were treated very courteously.”

The couple did contemplate staying in the country, where they had made friends and had built a life, but separation from family in the UK meant they decided to try again to return. “I got through every day by reminding myself that every single person goes through challenges at various times in their lives and that I was doing this for love,” she said. “Despite my best efforts the stress really started to take its toll on my health.”

Colin Yeo, a barrister specialising in immigration at Garden Court Chambers, is sceptical whether the draft deal will be able to effectively shut down Surinder Singh. “It is part of the draft which comes under ‘clarifications’, not treaty change, and Surinder Singh is a right which comes under the EU treaty,” he said. “Whether that ‘clarification’ will have any legal effect is questionable.”

After spending more than a year in Germany, Michael and Danielle now have a family settlement visa that allows them to set up home in the UK. “I feel like we belong somewhere for the first time since we’ve been married,” she said. “There is something about being away from a place for a long time that magnifies your love for it.”

It is the monetary value placed on her family life that Danielle said she found the hardest to accept. “People and planet are inherently more valuable than money,” she said. “It overlooks the fact that money is a human creation that should enable us to take better care of each other and the world we live in, and not be used as the prime motivator for tearing families apart.”

