Does anyone know if it’s possible to provisionally book a registrar?

I need some advice. I don’t live in the UK anymore but am getting married back home next year. I can’t book a registrar until my partner has a marriage visa and this can’t be done until 6 months beforehand. Does anyone know if it’s possible to provisionally book a registrar at all? I don’t want to leave it too late as I’m worried we wouldn’t be able to get married on our chosen date. Also, we’d like to ensure that we send our invites out in plenty of time. Thanks for your help.