Significance: Lead is a highly toxic element, and low-level environmental lead exposure remains a prime concern due its effects on neurodevelopment in children. It provides a well-researched example of the impact of human activities on environmental quality and the effectiveness of mitigation policies. Using recent and historical data on lead isotopic composition in London airborne particles, we show strong evidence that sources have not changed substantially since the ban in 1999 of leaded gasoline, the main source of environmental lead during the 20th century, suggesting that historical gasoline-derived lead remains an important source of lead in the urban environment due to its persistence and effective remobilization. Novel abatement policies need to be considered if this cycle is to be interrupted.