Roger is against this.
I think that in the future, a legal union, a dividing of the legal affairs of individuals who aren't necessarily lovers; perhaps life long companions would be a good thing. Many people now choose to live together, to share friendship who become life long partners.
There was the case in 2008 of two elderly sisters who had lived together their whole lives and who were fighting to be seen as a unit for inheritance tax reasons. Siblings cannot marry or form a Civil Partnership. Initimacy has nothing to do with it.
Prior to civil partnerships being offered to same sex couples, the fate of a surviving partner of same sex couples was a major problem. This is no less a problem for people who are life long companions who for reasons of family relationship cannot marry or join in a civil partnership.
I strongly disagree with Roger's stance. But the brother sister union he defined in his speech in the Commons on Monday it didn't seem to be incest he was referring to?