Social security claimants can be "friends with benefits" without losing their Centrelink benefits, a federal tribunal has ruled.

An attempt by the welfare agency to deny a Queensland woman a carer's allowance because she sometimes had sex with her housemate has been overruled by the Administrative Appeals Tribunal in a case that will be watched with interest by casual acquaintances around the nation.

Illustration: Cathy Wilcox

The tribunal, sitting in Brisbane, was faced with the tricky task of deciding the difference, for the purpose of Centrelink form-filling, between a de facto couple and "friends with benefits" as the woman, Ms T, described her relationship with a man known as Mr D.

Ms T claimed a carer's allowance in 2012 as her mother’s health deteriorated and she grew more dependent on her daughter, but Centrelink officials knocked back the application, deciding Mr D was Ms T’s live-in-lover.