Hi, I'm a British citizen wanting to apply for a China M Visa (multi entry, 12 months)

Hi, maybe it's difficult for you to get multiple entries M type in there, but you can have a try! You should prepare the required documents including passport and the copy, the filled-out application form, 2 passport-style photos, valid visa in there and the copy, bank statement, an invitation letter from business partner in China as well as other requirements.