Overstay in China due to another country's visa application

Hello,

Currently I have a residence permit in China which expires on July 15. Now I am on tight schedule to apply for the UK visa, and it is said that my UK application will take at least 3 weeks to process. I am afraid that my application processing might take somewhat longer time and cause my overstay in China.
Is application for another country's entry permit a good looking excuse for the China Immigration Office? Would I need to provide any documents upon the country exit to explain my overstay? And, most importantly, what will my penalty be?

Thanks a lot in advance,

Maria