Two elderly sisters are to mount a last legal challenge to enjoy the same tax rights as married and gay couples.
The Burden sisters have been fighting their case for years
Joyce and Sybil Burden, born in 1918 and 1925, have lived together in Marlborough all their lives.
Last year, they lost their battle for equal rights at the European Court of Human Rights, and now plan to appeal.
The sisters have willed their house to each other, but if one dies the other faces a large inheritance tax bill and may have to sell their shared home.
Judges will hear the appeal on Wednesday, with a decision due later this year.
The sisters argue that the UK Civil Partnership Act of 2004 breaches the European Convention on Human Rights.
The act allowed same sex couples the same rights as married heterosexual couples.
But the benefits, including passing property tax-free between partners, do not extend to co-habiting family members.
Their solicitor, Elizabeth Gedye, said they believed they deserved the same rights as such couples.
"They believe they should have the same rights because they feel that they've demonstrated a relationship that is as committed as any marriage, and maybe more so, and as committed as those that are in civil partnerships," she said.
"Their hope is that they will get an exemption so that on the first of them to die, no inheritance tax will be paid, thus making a significant saving and giving the second some security."
The spinsters have written to the Chancellor on the day before every Budget since 1976 seeking exemption from inheritance tax for family members.