How times and terms have changed. Twenty years ago, the term "partner" almost invariably referred to a business partner. If one meant, say, dancing partner, it had to be said explicitly.
Now, life partners have to become civil partners for their relationship and committment to be legally recognised, but only if they are gay (another word whose meaning has changed out of all recognition in most people's lifetimes). This is sexual discrimination as well as discrimination based on sexual orientation. Such discrimination should be illegal if it is not already so. Employers cannot use such discrimination towards their staff, so why should the state towards its citizens (or the monarchy towards its subjects)?
One corollary of this is that the two undertakings of Marriage and Civil Partnership should be synonymous together with their certificates, and state so. Anything else is a form of sexual discrimination.
The government can choose to be Humpty Dumpty, rather than a Nasty Numpty, on this ("Words mean exactly what I want them to mean" - Lewis Carrol), so why have they chosen in favour of discrimination?