Two Windrush sisters who describe themselves as “inseparable” face being split up by the Home Office because of their different dates of birth.

Bumi Thomas, 36, was told by the Home Office she had 14 days to leave the UK despite having spent more than half her life here. She shares a flat with her older sister Kemi, 38, in south-east London, and is a prominent singer on the UK jazz scene. The sisters say they are devoted to each other.

The family’s roots are in Nigeria. The sisters’ grandfather arrived in the UK from Nigeria in the 1950s to work and study. Their parents, Lizzy and Segun Thomas, settled in Glasgow in 1974 and Kemi and Bumi were born there. Lizzy and Segun set up the first black hairdressing salon in the area, called Hairlinks. It became a social and cultural hub for Commonwealth citizens.

Kemi was born in December 1981 and qualified for British citizenship under the immigration rules at the time as a child born in the UK to parents from a former British colony. Bumi was born in June 1983, just a few months after changes to the immigration rules removed the right to British citizenship for this group of children.

Under the British Nationality Act, which came into force in 1983, a person born in the UK on or after 1 January of that year only became a British citizen automatically if one of their parents was settled, held indefinite leave to remain or right of abode or was British at the time of their birth.

Bumi said: “Because of an accident of the timing of my birth I have had a lifetime of fighting for my right to belong here.”

Bumi has made a Windrush application to remain in the UK and has lodged a separate appeal against the Home Office’s refusal of permission for her continued right to remain in the UK.

Like many of the Windrush generation, Bumi’s parents were not aware of the need to naturalise in the 1980s and assumed the family had the right to remain in the UK.

It was not until 2009, when Bumi wanted to travel abroad for a holiday and could not get a British passport, that she realised there was a problem. After various battles with the Home Office she was granted two periods of discretionary leave to remain. Last November she applied for settlement in the UK. She had had a British partner but her relationship with him ended. In June this year the Home Office rejected her application and told her she no longer had the right to remain in the UK now that she no longer had the British partner. Her appeal against this decision will be heard in the immigration tribunal later this month.

Kemi and Bumi’s parents moved back to Nigeria with their children when Bumi was three. Bumi returned to the UK when she was 18. Because she has not been continuously resident in the UK she does not meet all the Windrush criteria. However, she hopes the Home Office will take the “sympathetic and proactive approach” it has promised to take when resolving Windrush applications.

Bumi says she is distraught at the prospect of being forced out of the UK and not only being wrenched away from her beloved sister but also from her community and her career.

“My sister is my anchor and my best friend. We have always been there for each other,” said Bumi. “I can’t even consider the possibility of life without her.”

She added that her experience with the Home Office had been “destabilising”. “Living in this kind of limbo has been purgatory,” she said.

Kemi said: “As a sister Bumi is my pillar of strength and a source of joy and hope. I was gutted when I read the Home Office’s response threatening her with deportation. I am praying that my sister will be granted the right to live as a British citizen in the only country we know as home.”

Her solicitor, Jamie Bell of Duncan Lewis Solicitors, said: “Bumi Thomas truly represents the best that Britain has to offer. However, because of an accident of her birth she has been through a 10-year ordeal to demonstrate what she has always known herself to be, a British citizen. She has been failed by unfair and unyielding immigration laws.”

A Home Office spokesperson said: “All immigration applications are considered on their individual merits and on the basis of the evidence available.”