If the no impediment to marriage certificate is issued by your local registrars office and you go down the route of dropping it into the embassy in Beijing you do not have to send it off to the Foreign office legalisation dept in Milton Keynes and then to the Chinese embassy in London, and you do not need to do the single cert either. To get mine in Dorset all I had to tell the registrar was my ladies name, age and the name of the town/city we were to get married in, and that was that. The British embassy did the rest overnight! I can not recommend this way of doing it enough and it's cheap too!