Joy Williams lived with her partner Norman Martin for 18 years in a Dorset home which they jointly owned, but she faced losing his half of the property when he died without changing his will.
Mr Martin’s half of the property automatically passed to his estranged wife, until Ms Williams took the case to County Court where a judge overturned the ruling in her favour.
Nadia Davis, head of the Family Law department at Martin-Kaye Solicitors in Telford, said: “It is clear that Britain’s current laws on cohabiting couples need to be brought into the 21st century.
“It’s never clear from one case to the next whether courts are going to allow a deceased person’s estate to pass on to a surviving cohabiting partner – even if they effectively lived together as husband and wife – so the situation certainly needs clarifying.”
She added: “Of course, the trauma of taking cases such as this through the courts can be easily avoided if couples who live together without being married ensure they have all the appropriate cohabitation agreements in place, and up-to-date wills.
"As the law stands right now, there is no such thing as a common-law husband or wife, and couples who live together do not automatically have the same rights as a married couple or those in a civil partnership.
“The last thing anyone wants to do, when they are dealing with the loss of a partner, is to find themselves being dragged through the courts in what is bound to be an emotionally exhausting – and potentially expensive – battle.
"Until the law on cohabitation is clarified, unmarried couples who live together should ensure they have agreements in place outlining who owns property and how bills are divided.
“People should always ensure that their wills are up to date and reflect their wishes, particularly if their circumstances or relationships change. It’s no good assuming that just because you live with someone that they will automatically inherit after your death – the system just doesn’t work like that.”