On the mean streets of Glasgow, where every vote is being fought over to keep Scotland in or out of the union, there's one man driving a black cab who is waging his own personal independence campaign.
When the meter clicks on, those who flag down this particular taxi may not know what they have let themselves in for. They can forget all expectation of a polite silence: the tribal political war that has been waged throughout Scotland for the past two years, will, for any passenger stepping into this black taxi cab, suddenly become confined, claustrophobic and in-your-face.
Glasgow has a fleet of 900 black cabs. It's the largest in Scotland. Glasgow Taxis maintain all its drivers are "trained and certified to the highest standards". But there is a below-the-radar hunt in the association to find the lone driver, the mobile motivator who, according to some of his colleagues, thinks he is the secret weapon of Alex Salmond and the Yes campaign. "We've been handed no hard-line complaint over his antics," said one of the mystery campaigner's fellow taxi drivers, who added: "But nearly all of us have heard how he operates, what he gets up to, and how threatening he can be."
The descriptions are backed up by other cab drivers who have heard roughly the same story from passengers: "I had that pal of yours drive me a couple days ago. I felt I'd been assaulted. I'd barely got in the car when he shouted through the glass at me: 'Are you Yes or No?'"
What follows is usually far from traditional cab-driver chit-chat. One driver said, "We think the man's Yes arguments begin as soon as he knows his customer's leanings. One customer was shouted at on his way home after saying he was likely to support the Better Together pro-union side: "What? Are you daft? Are you a Tory or what? There's no future in leaving stuff the way it is. You know that, don't you? If you don't, you should."
Another driver said: "I've been told that with one fare, he [the lone campaigner] actually stopped the cab, and put the meter on hold so he turn round and conduct a face-to-face argument."
Another driver said one of the cabby's secrets is to tell passengers that "every Glasgow taxi driver is voting Yes", adding: "That isn't true. But he doesn't seem to care much."
One passenger told a driver: "There should be a flashing warning on that cab. I should complain, but the whole country is going daft at the moment. I'll be glad when it's all over."
An official at Glasgow Taxis said no complaint had been received and no disciplinary process was in place. Unofficially? One source said: "We know he's out there. Maybe he shouldn't be doing what he's doing. But hell, he's not exactly Rob Roy, is he?"
The Glasgow cabbie is not that alone in the taxi industry. Mark McGowan, known as the Artist Taxi Driver, is filming high-profile individuals connected to the independence debate and putting them on YouTube.
The comedian Frankie Boyle, who backs independence, told McGowan that he didn't think it would happen. Others interviewed include Tommy Sheridan, the former Scottish Socialist MSP, and George Galloway, the Respect MP. Mr McGowan has not had Sir Paul McCartney in his cab yet. If he had, the former Beatle might have told him he supported continuation of the Union.
Yesterday, Sir Paul became the latest celebrity to add his name to an open letter to the people of Scotland urging voters in September's referendum to "stay together". So far 50,000 have signed the letter, including Sir Mick Jagger and Professor Stephen Hawking.
The TV historian, Dan Snow, the campaign co-cordinator, announced the new signatory as the Let's Stay Together group sought support in Liverpool.
* This article was originally accompanied by a picture of a Glasgow taxi cab. It was used for illustrative purposes, rather than to suggest it was the cab driven by the man referred to in our report. However, the driver of that particular taxi has asked us to make this point clear and to clarify that he is not the person who has allegedly been trying to persuade his customers to vote 'yes' in the upcoming referendum.