Stays of 4 days or less

I am travelling to Beijing for 3.5 days in April and have been advised that there has been a recent change to the requiremnts. I am advised that for stays of 4 days or less I no longer need to apply for a visa in the UK before I leave and that I can obtain one on arrival in Beijing. Is this correct and if so what is the process and cost and what do I need to take with me to obtain it?