Scotland will vote to become independent within two years if the UK backs Brexit in the European Union referendum, former first minister Alex Salmond has claimed.

Mr Salmond, who was appearing on the first major TV debate of the EU referendum campaign, also hit out at fellow Remain campaigner chancellor George Osborne over the Treasury's predictions of "apocalypse" as the consequences of Brexit.

Remain campaigners seized on an admission by Ukip's Diane James that "we just don't know" whether Britons would require visas to travel in Europe.

The Leave camp - represented by Ms James and Tory former cabinet minister Liam Fox - focused on the impact of immigration and the amount of money paid to Brussels.

In the BBC debate, filmed in Glasgow in front of an audience of voters aged 18 to 29, Mr Salmond said Scotland would vote to sever ties with the UK by 2018 if it faced being "dragged" out of the EU.

The SNP MP said the second independence referendum "would have to be within the two year period of the UK negotiating to withdraw" from the EU following a Leave win on June 23.

"If you had the situation where Scotland in four weeks' time votes Remain and the rest of the UK or England drags Scotland out by voting to leave then that would justify, in my opinion, another referendum," he said.

"In the circumstances of Scotland being threatened with being dragged out of the EU against our will, I think the result would be 'Yes' this time."

Ukip deputy chairwoman Ms James was challenged by host Victoria Derbyshire about whether a visa system would be introduced for travel to and from the EU in the event of Brexit.

She said: "Victoria, we just don't know because we have a prime minister who has said there is no Plan B, he has not presented a single bit of detail as to what happens if we vote to leave, he has left it completely open."

She added: "I don't believe we will need visas. It's all part of the Project Fear, it's about 'if we leave, all of a sudden Fortress Europe puts up the barriers and stops all of this happening'."

Her comments came after Labour In campaign chief Alan Johnson questioned whether visas would be necessary.

"How are you going to differentiate between the Polish plumber and the Polish tourist? It means surely a system of visas and if you haven't got a system of visas then how are you going to deal with ... you are telling people we are going to stop free movement, but you are not going to introduce visas so free movement will still be there," he said.

"Unless you put a border and watchtowers on the border between the Republic of Ireland and Northern Ireland you are going to have people coming across there because it would then be an EU country and a non-EU country."

Dr Fox said: "I'm all for people being able to come as tourists freely into this country, but if they want to work in the UK they would need to get a work permit, just like somebody who came from outside the EU.

"It is not beyond the wit of man to allow tourists to travel freely but to make sure you have a work permit when you want to work."

Mr Salmond, despite being on the same side of the referendum debate as Tory Chancellor Mr Osborne, criticised the Government's tactics in the referendum debate.

"I don't go with the scaremongering stuff," he said. "The Treasury says it's going to be apocalypse if Britain left the European Union. I don't believe that, but I do believe what the Bank of England says which is that there will be less growth and less jobs."

The audience appeared to agree with Mr Salmond's assessment of the Treasury's work. When Derbyshire asked if they believed the forecast the majority of the audience - made up of Remain, Leave and undecided voters - said no.