One of Scotland’s leading academics has called Brexit “the most unhinged example of national self-sabotage in living memory”.

Sir Anton Muscatelli, principal of Glasgow University, said everyone in public moral life had a moral duty to soften Britain’s departure from the European Union.

The economist, who was one of the first to warn of the dangers of a no-deal Brexit, said those politicians who did not not try to limit the damage of a rupture in Britain’s trade relations would face the “harsh” judgment of history.

Stressing he was speaking privately, Sir Anton said: “Very few economies operate as stand-alone World Trade Organisation members and there has been no comparable experience of a member of a regional trade association or free-trade area crashing out of that area without agreement.

“So the UK crashing out of the EU would be a first. The consequences would be dire in terms of disruption not only to trade in manufactured goods, but in the short run to food supply in the UK, air travel, enforcement of existing contracts in other EU countries. The list goes on.”

Sir Anton was speaking at a summit organised by Glasgow City Council on how Clydeside businesses and institutions, including the local authority itself, can brace themselves for economic uncertainty.

His language moved well beyond the normally diplomatic advice of a public intellectual. He said: “In my view, a hard Brexit would represent the most unhinged example of national self-sabotage in living memory – and everyone in public life has a duty, a moral obligation, to do what we can to prevent it.

“Any politician refusing to try – who won’t even attempt to soften the pain of Brexit by making the case for single market membership which all logic tells them is the right thing to do – is guilty of a serious dereliction of duty.

“And if their failure of leadership sets our economy and our society back for generations, history will judge them very harshly indeed.”

Glasgow City Council has commissioned analysis from Strathclyde University’s Fraser of Allander Institute showing that some 40,000 jobs in the city region depend on EU links.

Sir Anton has been advising the Scottish Government on Brexit and cited figures showing that the worst case scenario leaving the EU could cost Scotland more than 12 billion in lost economic growth. Economists call this a “headwind”, a drag on the economy whether it is growing or shrinking. “We simply cannot allow this to happen,” he said. Sir Anton believes there is now a “15-20 per cent” chance of a cliff edge, no deal Brexit.

The economist, like many others had been dismissed as a scaremonger. Now, he said, Project Fear had become “Project Fact”. Theresa May’s Chequers deal - her compromise offer to the EU hated by Tory Eurosceptics - was “dead”.

Lord John Kerr, the former UK diplomat who drafted the now infamous “Article 50” - the technical means by which Britain looks set to leave the EU - agreed Mrs May’s plan was lost.

But he told the same conference that it was not too late for the UK to change its mind. “Legally, we have not burnt our boats yet,” he said.

Glasgow-educated Lord Kerr is campaigning for a second referendum on the EU and believes article 50 - due to end the UK’s membership of the EU next spring - can be put on hold pending such a vote.

The politics around a “People’s Vote” remains complex with both main UK parties split. Lord Kerr warned that a “heavy responsibility” would fall on the third party in Westminster, the SNP, to help get any such second referendum through the Commons.