UK passport holder, resident in UAE

I live in Dubai where the China Embassy no longer process the visa themselves, but the out-sourced Visa-processing-firm WILL NOT process a 10yr Q2-Visa (Spouse), they will only accept application each year charging AED700/$200 each application.
We will travel on vacation to UK this summertime to visit family (wife easily got her 10yr UK visa already). Can I apply for Urgent/Express to submit/collect whilst travelling through London?
Wife is Chinese and our son has UK passport with 5yr PRC travel document.