In the presence of a warming climate, the urban climate becomes more important for city planners and architects working on methods to reduce near surface temperatures in order to enhance human comfort in the urban environment. The LUCID project (The Development of a Local Urban Climate Model and its Application to the Intelligent Design of Cities) brings together meteorologists, building scientists, urban modellers and epidemiologists in order to investigate the physical processes responsible for the London urban heat island and to derive planning strategies for future energy use and building and green space layout within cities. As part of this we are using the Met Office Unified Model with the new urban scheme MORUSES to perform long-term simulations over London. Early results will be reported comparing the simulations with a large network of measurements focusing on the hot summers 2003 and 2006.