Swh, your assessment is not accurate people do not shop around at all for a negative result, upon testing positive by any provider it is mandated that you stay at home for 2 weeks in the U.K.
I recently did a test to travel to Dubai performed by Halo which sends its samples to Imperial College London, it’s also the same test used by airlines in the U.K. I very much doubt its any less accurate than a government lab in Hong Kong. It’s entirely possible that Hong Kong labs are throwing up false positives.