Removing all trade tariffs and barriers would help generate an annual £135bn uplift to the UK economy, according to a group of pro-Brexit economists.
A "hard" Brexit is "economically much superior to soft", argues Prof Patrick Minford, lead author of a report from Economists for Free Trade.
He says eliminating tariffs, either within free trade deals or unilaterally, would deliver huge gains.
Other economists say cutting barriers sets off a "race to the bottom".
Economist Dr Monique Ebell from the National Institute of Social and Economic Research (NIESR) says Prof Minford "ignores decades of evidence on how trade actually works".
Dr Ebell's own research showed that if the UK left the single market but made unilateral trade deals with major developing economies and the Anglosphere, it would only claw back about one-third of the 20-30% reduction in lost total trade by leaving the EU.
Dr Ebell says many of the trade barriers that Prof Minford argues to be removed are subtle, non-tariff barriers, such as agreed common standards.
Campaigners against a hard Brexit said the plan amounts to "economic suicide".