Competing interests: The BMJ has judged that there are no disqualifying financial ties to commercial companies. The authors declare the following other interests: MD-W is a member of the BMJ International Advisory Board and the BMJ Commission on the Future of the NHS. She is an unremunerated co-founder and director of THIS Labs. Further details of The BMJ policy on financial interests are here: https://www.bmj.com/about-bmj/resources-authors/forms-policies-and-checklists/declaration-competing-interests.