Two elderly sisters from Wiltshire who have spent decades fighting for tax rights enjoyed by married and gay couples are due to learn if they have finally changed UK inheritance laws.

Joyce Burden, 99, and her 82-year old sister Sybil have lived together all their lives.

And since the 1970s they have worried about the crippling inheritance tax costs when one of them dies and has to sell their jointly-owned four-bedroom house in Marlborough.

Human Rights judges in Strasbourg will decide whether they should benefit from the same inheritance tax exemption given to married couples or "civil partners" when property passes between them.

The Burdens started writing to the Chancellor of the Exchequer in 1976 urging that cohabiting family members should be treated the same as married couples for inheritance tax purposes.

They repeated the plea in follow-up letters every year before Budget Day, without success.

Finally, when the UK Civil Partnership Act of 2004 recognised gay and lesbian couples for inheritance tax purposes, the sisters turned to the European Court of Human Rights.

Their lawyers argued that Act breaches Human Rights Convention articles outlawing discrimination and guaranteeing the "protection of property".

The sisters lost the case by the narrowest of margins - a 4-3 vote of the seven-judge court.

They appealed to the 17-member Grand Chamber of the Human Rights Court was heard last year which rules later. If they lose they know that, when one of them dies, the surviving sister will have to sell their four-bedroom house, valued in 2006 at GBP875,000, to pay the 40 per cent inheritance tax on its value above GBP300,000.