Unfortunately nothing could be done, once HK was China territory. Enforcing the domestic policies of an SAR inside of China was completely unfeasibly for the UK

Unfortunately nothing could be done, once HK was China territory. Enforcing the domestic policies of an SAR inside of China was completely unfeasibly for the UK and they knew it when they signed it. Zhao Ziyang (CCP chairman at the time), who signed the treaty, was a reformist and if he had remained in power and China continued down that path, things might have ended very differently for HK. Unfortunately the hardliners won out after the Tiananmen Square protests and he was removed from power.