I am due to travel to China to trek the Great Wall at the end of April for approx 10 days.

I understand I have to make an appointment to visit the Embassy in London and leave my passport for the visa to be issued. Can you please tell me how long it will take to have it sent back to me? I need my passport for other travel both at the beginning and end of March, so need to have my passport back in time for both trips. Alternatively, I can wait until beginning of April, if I can guarantee having passport back in time for China trip on 26th April. Please advise of my best option. Many thanks