Living permanently in China as a British subject

I don't think you an reside in China immidiately after your marriage with your Chinese girl friend. After your marriage, you will be able to stay in China for at most 180 days for each entry, adn then apply for an extension of 30 days stay twice. Then you will have to apply for another Chinese family visiting visa. You have to repeated this until you have lived in China for 5 years continously, you can apply for a permenant residence permit of China.