In most situations, you do need an original marriage certificate to get divorced in the UK. If you got married in England or Wales, it is sometimes possible to request a further copy be reissued if you can’t find your original certificate.
If you got married abroad, it might be possible to get a further copy issued, and you would need to seek guidance from the local authority that conducted the wedding ceremony or registered the marriage.
If your marriage certificate is not in English, you will also need to get a copy fully translated into English before you can issue your divorce petition.
If you cannot find your marriage certificate, it might be possible to still apply for divorce in some situations. You would however need to issue a separate application alongside your divorce petition. It is rare that the Court would allow a petition for divorce without a valid marriage certificate, and you would need expert legal advice before pursuing such an application.