This review describes historical iodine deficiency in the U.K., gives current information on dietary sources of iodine and summarises recent evidence of iodine deficiency and its association with child neurodevelopment. Iodine is required for the production of thyroid hormones that are needed for brain development, particularly during pregnancy. Iodine deficiency is a leading cause of preventable brain damage worldwide and is associated with impaired cognitive function. Despite a global focus on the elimination of iodine deficiency, iodine is a largely overlooked nutrient in the U.K., a situation we have endeavoured to address through a series of studies. Although the U.K. has been considered iodine-sufficient for many years, there is now concern that iodine deficiency may be prevalent, particularly in pregnant women and women of childbearing age; indeed we found mild-to-moderate iodine deficiency in pregnant women in Surrey. As the major dietary source of iodine in the U.K. is milk and dairy produce, it is relevant to note that we have found the iodine concentration of organic milk to be over 40% lower than that of conventional milk. In contrast to many countries, iodised table salt is unlikely to contribute to U.K. iodine intake as we have shown that its availability is low in grocery stores. This situation is of concern as the level of U.K. iodine deficiency is such that it is associated with adverse effects on offspring neurological development; we demonstrated a higher risk of low IQ and poorer reading-accuracy scores in U.K. children born to mothers who were iodine-deficient during pregnancy. Given our findings and those of others, iodine status in the U.K. population should be monitored, particularly in vulnerable subgroups such as pregnant women and children.