In The Big Smoke (1987), Brimblecombe retraces the development of air pollution controls in London since the middle ages. Then as now, free trade and social policy goals have clashed. Today, London is experimenting with a mix of incentive (Mayor’s Air quality fund), systemic (transport policy) and limitative (zero emission zone) means to address climate change. It has to include a factor absent in previous times: the policies set at supranational and national levels. Before Brexit, London had an ally in the EU: the Commission started proceedings against the UK for breaching pollution thresholds in London. After Brexit, the UK government aims to set up an enforcement Office for Environmental Protection to centralise power in the hand of the Executive. This leads to suggest that at a time when the limits of the UK constitution are tested, entrenching local powers and governance in a potential constitution may be needed to ensure a sustainable future from bottom up.