There is to be a tax concession for some married couples. I think the government may be overreaching itself.
I doubt whether the relationship between two people need concern anyone but themselves. There are many possible relationship between people yet the government has singled out for approval relationships between just two people. Until recently the people had to be of opposite gender. That has been liberalised to any two people regardless of gender, but why just two? Groups of three or more people sometimes live together in happy partnerships.
When two people have children it is a matter of public concern that the parents co-operate to care for their children, though I'm not sure how responsible parenthood could be rewarded through the tax system, without penalising the children of uncaring parents, but where there are no children partnership arrangements should be by civil contract drawn up to suit the people concerned.
That leaves the question of inheritance; bequests to partners are exempt from inheritance tax. Inheritance tax has always seemed to me a particularly spiteful tax, so I should be happy for it to be abolished, but failing that everyone could be allowed to designate just one person whose inheritance from them would be tax free.