Gabriel Felbermayr, president of the Kiel Institute for World Economy, pleaded for Brexit to be scrapped and exit negotiations to restarted from scratch. He also argued that the EU exit and future relations should be negotiated at the same time, despite Brussels bosses insisting future relations, like trade, be negotiated after the UK exits the bloc.
Mr Felbermayr also insisted there would not have be border controls and custom duties even if the UK leaves the EU without a deal.
He said tariffs for other states would also have to be lowered, in accordance of World Trade Organisation rules.
Mr Felbermayr told German Sunday newspaper Frankfurter Allgemeine: “Even a hard Brexit can be done without much damage if it is executed in a soft way.
“You can just wave the trucks through on the border, then there will not be any queues at the border.
“And of course you could just do without customs duties.”
The economist also offered a damning outlook on the future of the EU without the UK, saying that the Brussels bloc would be “less dynamic and less open”.
He said: “I’m not optimistic.
“Without the British, the EU will be less dynamic, less open, more centrally organised and will grow less strongly, which may please some, but I find that regrettable.
“It could indeed be the case that such a centralised, statist Europe may develop slower than the UK.”
Prime Minister Theresa May is trying to push Brexit back until June 30 at the latest, with the possibility of an early exit if she can get a deal through Parliament.
The current default outcome is for the UK to leave the EU this week at 11pm on 12 April without a deal, unless Mrs May can arrange an extension.
Additional reporting by Monika Pallenberg