Not all serious economists (who we can assume voted Leave) agree that Brexit is going to be economically harmful to the UK. Not all serious economic analyses suggest that Brexit will leave the UK permanently and materially poorer.
The argument can be taken up with the following who we can assume voted (if they are or would be UK citizens) to leave the EU, and some of whom might well have some understanding of the intricacies of trade deals.
Roger Bootle, Managing Director of Capital Economics, and Gerard Lyons, Economic advisor to the Mayor of London and former Chief Economist of Standard Chartered Bank. Ruth Lea, Warwick Lightfoot, Neil MacKinnon, Ryan Bourne, Head of Public Policy, Institute of Economic Affairs, Keith Boyfield, Executive Director, Keith Boyfield Associates, Professor Tim Congdon, Founder, International Monetary Research Ltd, Sean Corrigan, Hinde Capital, Mike Denham, Research Fellow, The TaxPayers’ Alliance, Bryan Gould, Former Labour Shadow Cabinet member & former vice-Chancellor, University of Waikato, Dr David Green, Chief Executive, CIVITAS, Dr Graham Gudgin, University of Cambridge, Dr. Oliver Hartwich, Executive Director, The New Zealand Initiative,Damon de Laszlo, Chairman, Economic Research Council, Graeme Leach, Former Chief Economist, Institute of Directors, Andrew Lilico, Chairman, Economists for Britain, Neil MacKinnon, Global Macro Strategist, VTB Capital,Dr Eileen Marshall, IEA Advisory Council, Professor Kent Matthews, Associate Dean for Engagement & Professor of Money and Banking, Cardiff University, Michael Petley, Chief Investment Officer, ECU Group, John Mills, Chairman and Founder of JML,Professor Patrick Minford, Professor of Economics, Cardiff Business School, Iain Murray, Vice President for Strategy, Competitive Enterprise Institute (Washington DC),David Myddelton, Professor D.R. Myddelton, Emeritus Professor of Finance and Accounting, Cranfield School of Management.Ross Parker, Brian Reading, former economics adviser to Edward Heath, Professor Colin Robinson, Advisory Council Institute of Economic Affairs & Emeritus Professor, Surrey University, Matthew Sinclair, Senior Consultant, Europe Economics, Professor Phil Whyman, Professor of Economics, Business, Economics and International Business, University of Central Lancashire,Dr Geoffrey Wyatt, Heriot-Watt University
https://forbritain.org/economists/supporters/