We are investigating how leading cities set whole-lifecycle-carbon (WLC) limits for new buildings, so London can strengthen its own policy in the coming update of the London Plan. Working with the Climate Change Mitigation Team we are reviewing WLC regulations in Oslo, Toronto, Vancouver and Helsinki, interviewing city officials and industry actors, and analysing London’s own WLC assessment database. We will benchmark the best-performing housing, office and public-building projects of the last eight years, convene a round-table with developers and NGOs, and distil the findings into clear guidance on ambitious yet just WLC targets. The result will equip London to keep global leadership on low-carbon construction and provide a model for national policy.