A quick explanation of civil partnerships

Civil partnerships in the United Kingdom, granted under the Civil Partnership Act 2004, allow same-sex couples to obtain essentially the same rights and responsibilities as civil marriage.[1] Civil partners are entitled to the same property rights as married opposite-sex couples, the same exemption as married couples on inheritance tax, social security and pension benefits, and also the ability to get parental responsibility for a partner's children,[2] as well as responsibility for reasonable maintenance of one's partner and their children, tenancy rights, full life insurance recognition, next of kin rights in hospitals, and others. There is a formal process for dissolving partnerships akin to divorce.

Please do not that it does say allow same-sex couples to obtain essentially the same rights and responsibilities as civil marriage. Meaning they have the same rights. Not more.

It is true that cohabiting siblings are denied the right to civil partnerships. But they are also denied the right to marry. Whether siblings should be allowed to marry is a whole different question and absolutely bugger all to do with the thread premise anyway. But it doesn't surprise me at all that a thread contaminated by our resident bigot turns to sexual preferences as usual. Says a lot really.