International migration of healthcare workers is well established and has become a means of maintaining service quality in many high income countries. In recent years, there has been a dramatic increase in recruitment of health personnel who have been trained abroad, including from the poorest countries in the world. In this article, using General Medical Council (GMC) data, we chart the growth in numbers of international staff working in the United Kingdom, where since 2018, over half of all new GMC registrations have been of doctors trained abroad. There is evidence that this migration of health staff results in poorer health service provision in low and middle income countries, as well as substantial economic impacts in these countries that have invested in training their health workforce. Recruiting governments have argued that remittances compensate for the loss of personnel, and that training opportunities can enable skills transfer to countries with weaker health systems. However, we found that the costs to the source countries dwarfed remittances, and that only a tiny fraction of people who move to take up posts in wealthier countries ever return to their countries of origin to work. We conclude that in addition to the investment in health systems (and workforce development) in low and middle income countries as part of Official Development Assistance for Health, there is an urgent need to increase training of nurses and doctors so that damaging migration is no longer relied upon to fill gaps in healthcare personnel.