The repercussions of the passage and promulgation in Hong Kong of the 2020 National Security Law (NSL) have been global in reach. Hong Kong featured prominently as the Trump Administration in the United States and Beijing teetered on the brink of a new Cold War. The National Security Law marked also a downward spiral in Sino-British relations amidst a wider backlash from, amongst others, the ‘Five Eyes’ alliance nations, comprising the US, the UK, Canada, Australia and New Zealand. This chapter describes the controversy over the 2020 law and the Sino-British exchanges which took place around it, both before and after its passage.