A hard Brexit could have a "pretty catastrophic" impact on the UK, a senior academic has warned, as he called for the free movement of people to continue temporarily after the country has left the European Union.

Professor Anton Muscatelli, the principal and vice chancellor of Glasgow University, argued that there should be "some sort of single market solution, at the very least as a transition".

The leading academic, who chairs First Minister Nicola Sturgeon's group of advisers on Brexit, also insisted that the UK should allow for different parts of the UK and different sectors to adopt varying policies on immigration.

This is something the Scottish Government has been pressing for, but Prof Muscatelli said the UK Government was "not being very receptive" to this at the moment.

Despite that, he said: "As experts I think we have a duty to point out where the flaws are in the hard Brexit argument."

Prof Muscatelli spoke out at a business breakfast organised by the Sunday Times Scotland, looking at the impact leaving the EU will have on skills and migration.

He told the event in Glasgow: "We are actually heading in my view for a pretty catastrophic outcome unless we have a relatively soft Brexit.

"I still think some sort of single market solution, at the very least as a transition, is frankly the best thing we can even hope for. Because you're not going to get a negotiated free trade agreement in two years' time, it's a complete fantasy.

"The best we can hope for is some transitory deal which will mean freedom of movement in the short run, which will then give you a platform for a longer discussion whether it is along the Swiss lines or yet another model that is still to be invented."

Switzerland, despite not being a member of the EU, has adopted a number of European laws to give it some access to the single market.

Prof Muscatelli also argued a blanket policy on immigration post-Brexit would be wrong.

"I think we need both a sectoral and a regional differentiated approach," he said.

Different nations and regions of the UK will have different skills shortages that they need to attract workers to fill, as will different sectors of the economy, the academic said.

He continued: "It's a huge task to put that post-Brexit structure in place, but certainly a differentiated approach by nation, region and sector I think might be the sensible way to go."

He added: "I haven't seen any evidence they (the UK Government) are likely to be sympathetic to this - that doesn't mean if it's right we shouldn't continue to argue for a differentiated approach.

"I do think it's something we will need to get our heads around because at the moment the UK hasn't had to confront since we have part of the European free movement area what we do around low and middle levels skills. They're not being very receptive at the moment but I think we have to continue making the case."

Dr Peter Bennie, the chairman of the British Medical Association in Scotland, said: "We do already have the bare bones of a skeleton of the ability to have different migration policies for different parts of the UK. There's a UK shortage occupation list, which includes a number of medical specialities where we simply don't have enough home graduates to fill those places at present. That's updated every couple of years.

"And there's a separate and additional Scottish shortage occupation list, which includes additional specialities. And it seems to me that that works very smoothly already for non-EU, non-EEA citizens.

"Therefore we are in a position where we've got at least the bones of that kind of structure and I think it could work."

However, former Labour government minister Tom Harris, who was the Vote Leave Scottish campaign director, said leaving the EU would mean politicians would have to "put their money where their mouth is" regarding better training.

Mr Harris argued: "For the first time our politicians are living in an environment where there is at least a possibility that if we don't train up Scottish youngsters to fulfil those roles we may not be able to rely on an unending supply of foreign workers to do those jobs for us.

"It puts a huge amount of pressure on politicians and it's something we should welcome, that for the first time in a generation these politicians are actually going to have to put their money where their mouth is and actually deliver on training of the indigenous population.

"They've been allowed to ignore that for too long because they've always been aware the safety net of EU immigration has been there."