A teenager who fears being subjected to female circumcision if returned to Sierra Leone has been granted asylum.
Female circumcision remains widespread in parts of the world
Five Law Lords overturned decisions by an Immigration Appeal Tribunal and the Court of Appeal, who ruled asylum laws did not apply to Zainab Fornah, 18.
The Refugee Convention says successful asylum seekers must come from a social group fearing persecution.
The Law Lords ruled female members of tribes where female genital mutilation was almost universal were such a group.
Baroness Hale of Richmond added it was a mystery why the case had reached the House of Lords as it was so "blindingly obvious" that asylum laws applied.
Last year the Court of Appeal ruled young women facing female genital mutilation could not be considered as "a social group fearing persecution" under the terms of the convention.
That was because the custom was so widespread in Sierra Leone and so bound up with its culture and traditions.
But on Wednesday Lord Bingham of Cornhill ruled that women in Sierra Leone were clearly "a group of persons sharing a common characteristic which, without a fundamental change in social mores, is unchangeable - namely a position of social inferiority as compared with men".
He added: "They are perceived by society as inferior. That is true of all women, those who accept or willingly embrace their inferior position and those who do not."
Female genital mutilation was an extreme manifestation of the discrimination to which all women were subjected in Sierra Leone, Lord Bingham added.
The practice had been internationally condemned as cruel, discriminatory and degrading and was against the law in this country, he said.
Female circumcision is legal in Sierra Leone and often performed before puberty.
Up to 90% of women have faced the procedure in the west African country, which sees part or all of the clitoris surgically removed, often resulting in reduced or no sexual feeling.
The operation is carried out, sometimes forcibly, on as many as 6,000 girls a day worldwide and health organisations report subsequent health problems.
Women carry out the surgery as part of an initiation rite to adulthood.
Lord Bingham said: "The operation, often very crudely performed, causes excruciating pain.
"It can give rise to serious long-term ill effects, physical and mental, and it is sometimes fatal.
"Even the lower classes of Sierra Leonean society regard uninitiated indigenous women as an abomination fit only for the worst sort of sexual exploitation."
The UN Refugee Agency's UK representative, Bemma Donkoh, told BBC News the agency had "consistently advocated that the refugee definition, if properly interpreted, can encompass women who have been persecuted for gender-related reasons".
"Significantly, all the parties involved in this case accepted the fact that female genital mutilation constitutes a particularly horrendous form of treatment and a violation of human rights that amounts to persecution," she added.
The Law Lords' judgment would provide "invaluable guidance on the interpretation of the refugee definition as set out in the 1951 Refugee Convention", Ms Donkoh said.
What "membership of a social group" meant in the context of the convention's definition of refugees had been the subject of "much consideration and analysis", she added.
"This judgment has greatly assisted in interpreting this part of the refugee convention."