"Are you going to take his name when married? If yes, change your name by deedpoll now. Everyone has the same name, everyone wins"
ER no.. how does the OP win, worst comes to worst and the marriage is delayed, then put back, then another PG.. He gets to have a perfect little family with zero legal protection for the DC.
If he wants the right thing, the right appearance the answer is simple, put a ring on her finger. Or at least get it done on paper. The actual party can come later.
I have 4 friends that are not married to the fathers, yet to all outsiders they look as though they would be, big house, big careers, all the trimmings etc, and only one of us kept the DC names as her surname. All of them have issues about the fact that the P never got round to marrying her.
Why on earth SHOULD we move heaven and earth, carry the baby, end up doing the bulk of the caring, keeping house, putting jobs, life etc on hold, and change our names to make HIM look as HE has done the right thing by us?
It IS embarrassing not to have the same surname, it invites questions or comments, and heaven help you if the other name isn't indigenous to the country....
Why SHOULD it be automatically assumed that the DC have HIS surname, even if he hasn't married their mother? Why, when she is the one carrying them, nurturing them and losing the sleep, should she change her name by deed poll, for his reputation? What about hers?
In the past women wouldn't have lived with their P, they would not have had DC with a P, only ever after marriage. Why should men get us to do all the running about when they are not doing any running themselves.
If you register your DC in your name until you get married, once you do so the change is permitted automatically and free IIRC.
It IS a big issue. Once you have DC with men who are like this, you lose all bargaining power.