I'm a Lesbian Couple: Starting a Family in the UK

HFEA-licensed clinic + known or anonymous donor

The simplest, most protected route. With treatment at a licensed clinic, the birth mother signs Form WP and her partner signs Form PP before treatment begins — this makes the partner the child's legal second parent from conception. Unlike some other countries, this route doesn't require the couple to be married or in a civil partnership — it just requires a licensed clinic and the right paperwork done in advance. The forms don't skip any paperwork on your end, though: you still need to register the birth in person at your local register office within 42 days, the same as any parent — what the forms do is entitle your partner to be named as the second parent on the birth certificate when you do.

Known donor via DIY/home insemination

The same known donor, but conception happens outside a licensed clinic. This changes the legal picture completely: the donor becomes the legal father by default, and the non-birth partner has no automatic legal parenthood claim at all, regardless of marriage or how long the couple has been together. She would need to adopt the child to secure legal parenthood — a slower, more involved process than simply using a licensed clinic in the first place. The donor, meanwhile, could be pursued for child support through the Child Maintenance Service (CMS), or could himself apply for a Child Arrangements Order seeking contact.