Competing interests: MG voted against Brexit in the 2016 referendum. MMcK declares that, as a British citizen and resident, he will be adversely affected by Brexit in many ways, although to a lesser extent than others as he also holds a EU27 passport. He reports funding for research and expert advice from the European Commission, and is the immediate past president (unpaid) of the European Public Health Association. He is an unpaid adviser to Healthier in the EU and Scientists for EU, both campaigning for continued EU membership and has advised the UK Faculty of Public Health in their campaign for a “do no harm” amendment to the EU withdrawal bill. He voted against Brexit in the 2016 referendum. MMB is chairman of Best for Britain, a political campaign “fighting to keep the door open to EU membership.” FG is editor in chief of The BMJ and responsible for all that it contains. She voted against Brexit in the 2016 referendum.