The ruling from Panama's top court is widely seen as a victory for the Trump administration, which is seeking to counter any Chinese influence in the region.
China rolled out a new work plan to boost services consumption as stimulus measures to boost households spending on goods have so far done little to lift demand.
The rout was triggered by an announcement on Tuesday by index provider MSCI, warning of a potential downgrade of the country to "frontier" market status.
Starmer is on a 4-day visit to China this week, the first trip by a British leader in eight years, signaling an attempt at resetting the bilateral ties.