144 hour free transit - dilemma!!!!! PLEASE HELP

I want to make use of the 144 hour free transit in Shanghai. This essentially allows you to travel from country a to china and then onto country b. A and b have to be different in order to qualify for the visa. I have done this before without issue. However this time is slightly different, I am travelling from the US to China with a connecting flight in London, staying a few days and then flying out to UK as my final destination. The question is does my connection in London on the way count even though I would be staying airside? Hope that makes sense - please help!