A South African doctor and her British husband are living on either side of the Irish border because of what one MP called a “borderline unconstitutional” application of post-Brexit immigration rules.

Corrinne and Brett Giles live 25 miles apart in Donegal and Derry counties respectively, with Corrinne in a “constant state of anxiety” waiting for a family permit to join her husband in the UK.

The A&E doctor, who worked on the Covid frontline, is out of a job and “living out of a suitcase” because she felt she could not extend her contract in Ireland as she was imminently emigrating to the UK.

Eight months on, she faces having to go back to South Africa as her residency rights in Ireland come to an end. She could risk the threat of deportation if she was caught illegally entering Northern Ireland.

Since Britain left the EU, UK citizens’ non-British spouses need to apply for pre-settled status before 29 March next year if they want to return as a family to the country visa-free. They are eligible only if they get a new EU family permit for the UK first.

Before Brexit, Britons’ relatives could return to the UK at any time without visas under free movement laws that applied to EU and non-EU spouses. Post-Brexit, that route ended, but the UK government, under pressure, pledged to keep the visa-free door open until March next year, enabling non-British spouses to apply for pre-settled or settled status.

But their EU family permit ceased to be recognised after Brexit by the Home Office, which now requires applicants to be issued with a UK issued family permit.

After 15 years in South Africa, the Gileses moved to Ireland two years ago, wanting to be closer to family in the UK while Corrinne worked in Letterkenny university hospital’s A&E unit.

Their saga began eight months ago on starting to explore their options to move to England. They discovered there was a visa-free route for Corrinne under a Brexit side-deal which allows non-EU nationals entry to the UK as long as they first get a family permit from the Home Office.

Brett, who works in marketing, moved across the border to Derry in Northern Ireland, having read guidance on the government’s website that UK citizens should return to the UK before the end of December last year, to exercise his EU freedom of movement rights. The website said a family permit would take a few weeks to process, which he saw as a small price to pay.

Five months later, however, there is no sign of the family permit and no communication from the Home Office other than to say the application is in the system. Meanwhile Corrinne, 48, lives in a single room in Letterkenny and is unable to apply to fill health service vacancies in Ireland or in the NHS.

“I’m absolutely emotionally drained and exhausted mentally and physically,” she said. “I’m living in this constant state of anxiety every day, checking emails that will determine my future.

“All the time the gap in my working career is growing substantially. Being kept in the dark with absolutely no feedback or communication from the Home Office is absolute torture. I never in my wildest dreams thought that two years after coming to Europe, I would be sitting on the couch, unemployed, disillusioned, disheartened.

“All I want is a normal life. Also all my family are in the UK, my brothers, my sisters, my mum, and I’m completely alone in a foreign environment and it’s becoming increasingly difficult for me to continue this life.”

Brett’s MP, Colum Eastwood, who has been working with the couple, said they had been met with “obstinacy from the Home Office at every turn” and questioned “how the Home Office cannot … carry out the necessary checks in this timeframe”.

The Labour MP Peter Kyle, who is advocating for a constituent in a similar position, said: “The government has entirely forgotten that they are [here] to serve British citizens.”

At least a dozen other families have shared their stories with the Guardian, including a mother who has returned to the UK from France with her seven-year-old, separating her child from his French father who is also on the long Home Office waiting list; a gay British man desperate to return to the UK with his Italian partner of 26 years; and a German woman waiting since April for her permit to join her British husband.

“To be so hostile and obfuscatory towards a British citizen, to make it difficult for a British citizen to even get information on how to resolve a situation caused by government policy, is borderline unconstitutional,” said Kyle.

A Home Office spokesperson declined to comment on specific cases, saying: “Eligible family members of British citizens returning with them to the UK from the EU should apply for an EU Settlement Scheme family permit. Each case is considered as quickly as possible and on its individual merits but processing times can vary depending on the volume and complexity of applications.”

Cases were “considered in strict date of application order”, suggesting a five month backlog for Britons in the EU, and the Home Office would “continue to review staffing levels”, it said.