Exiting the European Union (EU) without a deal would have "stark, catastrophic and unavoidable" economic consequences, a leading academic has warned.

Professor Anton Muscatelli, principal of the University of Glasgow, urged the UK Government to avoid a "cliff-edge" Brexit regardless of the political costs.

Prof Muscatelli, who chairs the Scottish Government's Standing Council on Europe, also challenged public figures to make clear the benefits of migrants to the UK and Scottish economy.

Addressing an audience at the university's Bute Hall, he said: "There are three possible Brexit scenarios - the most negative of which is the 'cliff-edge Brexit', seeing the UK exit the EU without an agreement and reverting to WTO rules, which some estimates suggest could cost the UK economy as much as 9.4% of GDP by 2030.

"If this is the route the UK is forced to take, the economic consequences would be stark, catastrophic and unavoidable.

"The UK Government's idea of a 'Goldilocks Brexit' would see a standalone free trade agreement and a new strategic partnership - but even this would still constitute a 'hard Brexit' in economic terms, and it is difficult to see why the EU would agree to a bilateral system it has avoided in other situations.

"The other option is a 'European single market Brexit' which has seemingly been ruled out - but could come back into play at least as a transitional measure.

"While this would involve serious political costs for the UK Government and entail a reinterpretation of their own red-lines - it may be the only way the Prime Minister can avoid the UK economy falling over the Brexit cliff-edge."

Prof Muscatelli said a reduction in EU immigration would hit the labour supply for a range of sectors and could have a "severe" impact on the tax base in Scotland, where he said EU immigration had "gone some way to stabilising the Scottish population".

He said: "The vital importance of freedom of movement to Scotland and the UK's economic future is clear - the challenge now is for politicians and public figures from across the political spectrum to commit to extolling the virtues of migration and refusing to let the public debate be poisoned by some of the negative rhetoric we've seen in recent months.

"We have often been told by anti-immigrant politicians that they simply want a 'debate' on migration - the facts are absolutely clear and those of us who believe in the economic and social benefits of an open, welcoming society should not be shy about using them."