I've read somewhere that if a British man will get his CNI from UK, he has to wait for ten days whilst he is in UK then he can bring it here,submit to British embassy, wait for ten days then it will be released, then apply for marriage license, then 15 days again. That's why my fiancé and I thought that he needs to stay here for 25 days just to get married here, and we just decided to have our wedding in UK because it's impossible for him to stay here that long