The UK will remain united, an "armed forces alliance" will mean there is still a "British" army, an independent Scotland will share embassies worldwide with the rest of the UK and the Faslane base won't necessarily close to create a nuclear-free Scotland, because a future Holyrood government could vote to retain Trident. For Jim McColl, one of Scotland's richest men, there is little risk in Scotland voting to leave the union next week. "Things could be running the just the same as they are now," he says.

The assurances from Mr McColl – the billionaire head of 90 companies operating in 30 countries, whose CBC (Clyde Blowers Capital) business empire is headquartered near Glasgow – that the "United Kingdom will stay the same, with the Queen as its head of state", flies in the face of the stark warning from Alistair Darling, who heads the pro-union No campaign, that there will be "no turning back" if the Yes campaign triumphs.

Mr McColl's views, regularly discussed with Alex Salmond in his role as economic adviser to the First Minister, will shock many independence supporters who believe they are lining up to vote for a political earthquake, a clean break from Westminster; and for some life-long CND supporters, the long-held ambition is to close Faslane.

Mr McColl was in London for discussions with investors following his rescue of the ailing Ferguson shipyard in Port Glasgow and he spoke to The Independent on Sunday in the calm of the Grosvenor House Hotel before he flew back to Glasgow.

Although Mr McColl, 63, has not always been an advocate of independence, he accepts that during the 18 months of debate on the referendum, "the process has changed my views". But he accepts that if David Cameron had agreed to have a third question on the ballot paper, one that offered enhanced devolution powers, "then that is what we would have got – everyone would have voted for more powers, but remaining part of the UK".

In-or-out for Mr McColl centres on what he repeatedly calls "more fiscal powers". He says, in uncomplicated language, that "there is no scope for Scotland doing something that would stimulate job creation or attract businesses or support entrepreneurial activity because it doesn't have the levers to allow it to do that". In same precise tone, he attacks the Calman Commission that examined how devolution could be beefed up. He says the commission's brief "didn't allow it to come up with recommendations that would give Scotland an advantage over any other part of the UK".

Parts of the No campaign have attacked the proposed reduction of corporation tax in an independent Scotland as likely to reduce revenue, increase the rewards to "fat cat" big companies, and affect spending on social services. Mr McColl questions the logic. "If they are saying it's all going to the rich guys in big business – there is no big business in Scotland." Government-owned banks, he says, don't count.

What works for his companies operating in China and Canada – where R&D is deducted before tax, or where no corporation tax is paid in the first six years of a start-up – isn't happening in Scotland, he says. Government money for skills development and other assistance projects fails to reach its targets in Scotland, wasted in endless subcontracts. And the bigger picture? "There is something fundamentally wrong," he says, with the way Scotland is handed a share of UK spending. "It's 'here is your pocket money'. We are a wealthy dependent nation – that's what we are."

On oil, Mr McColl says aggressive stealth tax raids on income from the North Sea have left the oil companies uncertain of where the "next hit" is coming from and that an independent Scotland should "constitutionally" lock in a decade of "stable" lower tax rates to ensure greater investment.

Mr McColl, the son of a butcher, left school at 16 to become an apprentice in a leading Glasgow engineering firm – which he later bought. He went on to study technology, business and international accountancy at university and then created one of Scotland's leading business portfolios in a globally respected company.

His story points to an emotional attachment to independence and the concept of freedom. But, he says, "I'm just attached to the potential of Scotland being economically stronger than it is."

His dual perspectives, as a Scottish government adviser and a billionaire businessman, suggest that he should be able to spot scare tactics in the political yard fight better than others.

Surprisingly, he claims the biggest scare story is a Yes vote. " It's not this big, massive jump. This is a vote to have an independent parliament. At one extreme, things could be running the same as they are at the moment. There's an election in 2016 for the Scottish Parliament. [Before the deal on independence is agreed.] The main parties will need a manifesto. They'll need a Plan B – to say how they would run Scotland. None is disclosing this."

And before the Scottish 2016 poll, there will be next year's UK election. For Mr McColl, this means Ed Miliband, for example, can't be hostile to a common currency; there would be discussions on shared armed forces; and win-wins for both sides would emerge.