Getting a work visa for China from Japan

I'm a British citizen, and I have just accepted a job offer from a school in China (Shanghai) starting in September. So far I have found lots of conflicting information on how to apply for the entry permit and I just want to know the quickest and easiest way. I have my passport, university degree, proof of prior employment and I am applying for my background check. Can I apply without going back to England? If I leave now I would have to cancel my contract.