Taking as his inspiration an unrelated barb by a Russian official at the G20 summit that Britain was just a "small island", the Glaswegian business "Dragon" tweeted that we are a "great country made up of Scotland, England Wales & NI that should stick together as 1 & not separate [sic]".
Shortly after, he was back online to complain that he had been "attacked by racists" for his comments. "Why is it that nobody who believes in Independent Scotland can put forward an argument without bad language, insults or threats?" he wanted to know.
Bannatyne is one of a small circle of leading business people to have come out in support of either side. Yes Scotland and Better Together are both under mounting pressure to persuade business bosses to take the plunge.
In any election, the contenders' ability to get endorsements from business is always one of the yardsticks by which they are measured. New Labour arranged for a group of leading businessmen, including Tim Waterstone and Sir Gerry Robinson, to write a letter endorsing it in the run-up to the 1997 General Election.
And the SNP made much of receiving the backing of the likes of former RBS chairman Sir George Mathewson ahead of May 2007, before later giving him the chair of the Scottish Government's Council of Economic Advisers.
Independence is a slightly special case, of course, since the outcome will not be voted away four years later. Both sides say that self-made entrepreneurs are the most likely to support them, since they are less restricted by institutional conservatism.
Apart from Bannatyne, the handful of prominent businessmen openly on the unionist side have included Rupert Soames, head of temporary power supply group Aggreko; HSBC chairman Douglas Flint; Mackie's ice cream founder Maitland Mackie; Boyd Tunnock of biscuits and confectionery fame; Orion recruitment founder Alan Savage; and Ultimo lingerie owner Michelle Mone.
On the nationalist side, longstanding supporters Mathewson and Stagecoach boss Brian Souter have been joined by the likes of engineering tycoon Jim McColl, commercial property developer Dan Macdonald, Wise Property Care managing director Les Meikle, Aquamarine Power wave energy boss Martin McAdam and Tony Banks, chairman of care home company Balhousie Care Group.
And that's about it. Pretty much anyone else you can think of in Scottish business has yet to declare.
Phil Anderton, the former Heart of Midlothian Football Club chief executive who is the director of Better Together in charge of liaising with the business community, says: "If you look at the polls, you have got between 20% and 30% of people saying they are going to vote Yes for independence. If you have got a customer business, you don't want to alienate that group. And you have got shareholders to think about as well."
Business voices on both sides also variously cite time, staff sentiment and the "lack of reliable information" as reasons for their silence on the issue.
Then, of course, there is the ''abuse'' issue. Michelle Mone complained of similar internet attacks to Duncan Bannatyne after going online last year to announce that she would move her business headquarters to England if the Yes campaign succeeded.
When asked for an opinion on her experiences last week, she said she had decided not to discuss the subject and could not get off the phone quickly enough.
Maitland Mackie is another businessman who says he has had an unpleasant experience. "Within a day of putting my personal views out there, there were about 100 emails that came into the business.
"It was quite upsetting for the office, with people saying we will never buy your ice cream again and things like that. After a day it stopped, which made me think it was orchestrated," he says.
Anderton claims that ''independent research" shows that the vast majority of businesses in Scotland are against independence, echoing views expressed in public by figures including David Cameron.
A Mori poll late last year found that over two-thirds of business people thought that independence would negatively affect their businesses, while a survey in May by the Scottish Council for Development and Industry showed members of the think tank had concerns about things like an Anglo-Scottish currency union and there was no great enthusiasm for the SNP plan for lower corporation taxes.
However, the research does not all point in one direction.
A more recent survey by the Scottish Chambers of Commerce found that most businesses felt there was too little information to take a view, and Ernst & Young showed that investment was at a 15-year high despite the upcoming referendum.
On the other hand, there was a noticeable absence of senior SNP figures at the recent annual dinner of the Confederation of British Industry Scotland in Glasgow, while a good handful of senior politicians from the three leading unionist parties had been invited, including Deputy Prime Minister Nick Clegg, Scottish Labour leader Johann Lamont and Scottish Tory leader Ruth Davidson.
The CBI confirmed that Deputy First Minister Nicola Sturgeon had declined an invitation, citing other duties, but no other senior figure appears to have been invited in her place. CBI president Sir Mike Rake, meanwhile, used his podium address to criticise the independence option that night.
Phil Anderton says that his job is not so much about persuading the business community to back his cause as to come out of the shadows. He says he spends about two-thirds of his time either meeting people on the business circuit or fundraising, two roles which regularly overlap.
He is not keen to get into the specifics of how much time this involves or exactly who he has been meeting, declining to outline his last month's activities, for example. He makes reference to his old marketing days at Coca-Cola, when it was important not to give out information that could help Pepsi.
On the other side, SNP sources reckon that Yes Scotland runs about two opinion- shaping events for businesses every week on average alongside about two more run by the SNP.
The Yes campaign also encourages organisations all over Scotland to host neutral events where both sides speak, in the belief that the more people that listen to the arguments, the more people will buy into the independence cause. In all, sources estimate that this adds up to more than 365 events a year where their trained business representatives participate.
While they are resigned to many of the top business leaders staying out of the debate, they argue that a large number are either genuinely undecided or leaning towards the Yes camp. Contending that much suspicion from business has been extinguished by six years of good engagement from the Scottish Government, they also indicate that more big names are poised to declare in their favour in the coming months.
Blair Jenkins, head of Yes Scotland, says: "There are a series of well-known job creators who previously supported devo max, whereby all fiscal powers would reside in Scotland. In the absence of that option in any credible timeframe, they increasingly understand a Yes vote is now the best way forward.
"They are especially focused on engaging with what the powers of independence can mean for boosting jobs and investment. Some may choose to air their personal support for Yes later in the campaign and we'll spend time listening to them in the meantime.
"Some have or will choose to remain neutral in public. Others have chosen to begin the process early of publicly normalising support for independence amongst business leaders so their peers understand they are in good company."
The Yes camp also believes it has "stolen a march" on Better Together by launching Business For Scotland (BFS) a few months ago, which started as a group of about 350 business people from companies of different sizes who are backing independence.
Having announced in the summer that the number had reached 500, sources say that there will be another update on growing numbers in the coming weeks. Tony Banks, who is heavily involved in BFS, says that eight new businesses had signed up even on the day we spoke.
Banks also derides the CBI opposition, pointing out that he is a member of the association himself. "The CBI rolls out people from the southeast of England whose whole life is about making sure that the centre of the universe is the southeast of England. Why would anybody want to listen to them?"
The next milestone for both campaigns is the White Paper expected in November but now rumoured to be coming sooner.
Better Together says it is organising a group of business people - it won't say how many - to start engaging more with the media at the time the document is published.
The rationale is that there will be something more tangible to oppose by then. For the opposite reason, the Yes Scotland and Business For Scotland representatives will move to the fore at the same time too. Both sides will clearly be putting maximum pressure on their more cautious supporters to get involved.
Maitland Mackie could be speaking for either side when he says: "I think it's time people had the courage to speak out. I understand totally why it's difficult, but it's an awful tragedy this road we are being taken down and people should speak out."
With both sides adamant that they have the majority of business backing them, they cannot both be right. Whether a groundswell of briefcases on one side or the other shows that one was correct, or whether conservatism and fear keep most of those undeclared in the shadows, there will be little else to do but watch closely in the coming months.