To retain GGL, 40,000 TPs are required, at least 32,000 TPs should be earned through British Airways-marketed flights.
I can earn 2,500 TPs by BA Amex spending.
It left only 5,500 TPs for me to earn through travelling with other non-BA marketed flights.

I usally travel the LHR-HND route. I found that for the JAL operated flight with BA-marketed (BA coded) are much more expensive than the JAL operated flight without BA-marketed (only JAL coded). I don't think I will pay the extra money to earn extra TPs. What I can think is that, I will make the future booking by BA Holiday, so the tax and charges will be counted. Do you all have any more ideas to maximize TPs? Thank you.