In terms of rollout. UK is the ideal country to be the first: 1. Heavily impacted by Covid-19. 2. Centralised health care system makes it easier to compare results and efficiency. E.g. it's UK which figured out that dexamethasone is efficient against Covid https://www.who.int/news/item/16-06-2020-who-welcomes-prelim... 3. Developed country with great logistics.
While the healthcare is centralised, the data is not, and often poorly federated between a multitude of organisations. Scotland has unified this much more and is far better placed to monitor for efficacy and side effects.