OK not RTFT but a reason people want sperm donors via the clinic isn’t just to do with avoiding maintenance and keeping the donor anonymity until child is 18, but also because the sperm provided by a licensed UK clinic is guaranteed to be robust super A grade sperm, also free from STIs. Kind of like ‘medical grade’ sperm, IYSWIM.
It’s all exhaustively tested to make sure clinics only provide highly effective high quality sperm. That’s really very different, in terms of the actual chances of safely conceiving, from hoping to get pregnant with a man who has got someone pregnant at some point in time before. Or, a man who wants to coparent.
This very high standard of sperm used in clinics is partly why we have a lack of donated sperm in clinics from men from the UK. Because many men who might have applied years ago when there was life long donor anonymity via clinics now don’t apply, because all donors will need to be happy to be identifiable to the limited (by clinics) number of 18year olds they may have produced if their sperm had been used successfully.
From the remaining pool of potential donors who are happy to be identifiable in future, the vast majority are then screened out as donors after giving test samples. This is because their sperm is not of a high enough quality to be a donor via a clinic.
If the woman who wants to conceive by donation is 35+ years old, then in statistical terms, she would have the best chance if she uses high quality clinic-assured sperm.
There are also ways of getting reduced cost fertility treatment including IVF if they are serious about it, which have their own implications. (Like egg sharing schemes) though usually you have to be under 35 to be an egg donor in the UK. (again, for quality reasons so clinics can provide very good quality eggs.)
There are lots of websites with information about this- HFEA, Donor conception network etc.
(Incidentally there’s nothing to stop a willing egg or sperm donor going to donate via a licensed clinic with a couple they know, to become a known donor to that couple.
That allows everyone to have the legal protections of the legal donation relationship, rather than just the ‘donor’ becoming a biological father or mother of their baby without the legal protections if no clinic is involved.
But key point here is consent and your DH doesn’t want to be a donor at all so it’s absolutely fair enough that he isn’t one and no justification required.