On a toilet wall in Matt O'Connor's home near Winchester hangs a framed letter from the procurator fiscal of Fife, placed there to indicate the gravity of spirit with which O'Connor received it.

The missive forbids the 41-year-old activist from coming within 20 miles of the Forth rail bridge, a disproportionate if perhaps understandable precaution, given that O'Connor commended himself to posterity on September 13, 2004, when a member of his Fathers 4 Justice organisation scaled the frontage of Buckingham Palace dressed as Batman, and thereby, paradoxically, sealed forever O'Connor's reputation as the joker of the family law reform movement.

Whether the letter's desire to prevent a calamitous interface of Caped Crusader and titanic iron structure remains in effect is something O'Connor will discover in the weeks ahead, as he pursues his campaign to be elected mayor of London. At first, second and 37th glance, it's a strategy that even his quixotic opponent, Boris Johnson, would dismiss as a tad cracked: lobbying to become first citizen of London through poster campaigns in Edinburgh and, shortly, Glasgow and Aberdeen - campaigns attacked last week for their scabrous assertion that Londoners subsidise Scotland's superior social care.

Phase two will involve a guerrilla journey on the 11.15 from Waverley station to North Queensferry, during which the disputed territory of the Forth bridge will be crossed on the way towards Gordon Brown's constituency home. “It's a watch-this-space plan, that's all I'll say,” says O'Connor. “We're going to Fife and we're going to repatriate Gordon Brown. We've got all kinds of bits and pieces up our sleeves for the future.”

Do-or-die missions by means of First ScotRail commuter trains may not figure in the electoral strategies of Johnson or Ken Livingstone but, clearly, O'Connor is taking a singular tack entirely, to the extent that he's “not actually that bothered about becoming mayor” - which is handy, given that even the most generous forecasters say he has little chance of securing more than 1% of the vote next month. “Which is annoying, because they're all pretty woeful, really,” he says. “Boris is Mr Clueless, different haircut but the same guy underneath; there's Brian Paddick, who's Mr Faceless; and Mr Shameless in Ken Livingstone. But they have the resources to bamboozle Londoners. Livingstone and Boris have more money than God. I've got enough for a McDonald's drive-through.”

History, however, shows there's some method in O'Connor's madness. The founder of Fathers 4 Justice and a marketing and design executive by trade, he's been named in the past the 92nd most powerful man in Britain and the seventh-best communicator by GQ magazine, as well the 35th most powerful man in Britain under 50 by Esquire. Shortlisted for the Great Briton of the Year award in 2005, O'Connor was congratulated for using “great humour, eccentricity and innovation in raising awareness of a very serious social issue” - namely, that family law is skewed horribly against fathers.

At the same time, he has just declined an invitation to work with the British National party. His mayoral campaign, he says, is essentially a prelude to a full-time entry into politics in 2009. The anti-Scottish posters are an opening salvo in his battle for English pride.

Unveiled last week, one poster shows a Scot in a tartan terrorist's balaclava grabbing a fistful of cash beneath the slogan “Save London from Labour's Tartan Taxes”; the other has a kilted hairy flashing his pixellated nether parts with the instruction “Make Jock Strapped; Give London's Money Back.”

The campaign is certainly dubious, a jarring intrusion of lad's mag mentality into the usually placid, pedantic realms of political sloganeering. O'Connor is standing at the behest of the English Democrats, a cabal of narked letter-writers and real-life versions of the characters in Sunday evening BBC sitcoms, commonly bent upon the establishment of a parliament that's exclusively English. At a recent by-election in Lambeth, though, the party received just eight votes, fewer than the number who'd been required to fill out the nomination form.

“I'd rather eat my left testicle than be compared in any way with the BNP,” says O'Connor. “But in the political mainstream, the idea of England has been abandoned and there's a void. My hope is to help fill that void while stripping English nationalism of its far-right associations.

“If you think those ads are racist,” he adds, “speak to Alex Salmond and see if you can get him to condemn them. I'm sure he won't. They work in his favour - they underscore the need for two separate, distinct systems. How can helping the SNP be construed as a racist slur against Scots?”

Whether O'Connor has concocted this defence in the wake of the intense reaction to his posters is difficult to say. He's full of praise for the nimbleness of Salmond's administration and says the iconoclastic bitterness of Rab C Nesbitt has long been one of his greatest philosophical inspirations.

The Scots earn his deepest approbation; how can he truly hate the Scots, he asks, when he's half Irish? “You have to operate in the theatre of provocation if you want to compete with the big parties. It's quite depressing, I suppose, that I have to do a campaign like the tartan tax campaign to get noticed. I'd much rather be having proper intellectual debate with people on the issues. But you have to shoot towards the goalposts, and that's where they are these days. I don't have any problem with the Scots, far from it. It's just that I'd prefer friendly neighbours to a surly lodger living upstairs.”

Instead, his real target is the Labour government, whose Scottish prime minister, chancellor and Speaker effectively render it, he thinks, Scottish by birth, nature and inclination, notwithstanding the 587 MPs who do not represent Scottish constituencies.

In O'Connor's mind, since 1997 Scotland and the current Labour government have conspired to become synonyms for one another. Our political culture, he says, has been “perverted” by Labour to quash nationalism in Scotland and Wales, which were bought off with devolution.

One result, he says, is the silent English majority, for whom he is striving to provide a voice. You may have thought it already had one, if the Campaign for an English Parliament (CEP), recent events in Berwickupon-Tweed and the antics of Kelvin MacKenzie have been anything to judge by. But O'Connor inhabits a similar line of country, the we-only-want-what's-fair, social-service equivalence lobby. The difficulty with this argument, though, is that the facts and figures are moveable feasts, even when considering the relatively quotidian Barnett formula (which was anyway revealed last week to have been “written on the back of an envelope”). Nobody can agree on the stats, and they're complicated by a vast array of historic quirks and exceptions.

According to Oxford Economic Forecasting, £17.8billion flows from London annually to fund services elsewhere in Britain, though clearly only a proportion of that wealth is created by indigenous Londoners; vast tranches of cash flow into London to pay for central government; under international law, the bulk of North Sea oil arguably belongs to England, and so on and so forth.

The subject is like quicksilver, altered by the merest attempt to approach it. Not even forensic economists can agree on a proper allocation of the spoils. Like MacKenzie and the CEP, however, O'Connor is happy to yomp onto the blasted heath and coax the sparks of English self-determination into some kind of blaze, obviously with no particular time frame being applied to the process.

“The MacKenzie line about anti-Scottish resentment in the south of England is overstated,” he says. “It's a slow burn of a subject.”

Pressed on who he'd prefer to see as London mayor, it it ends up not being himself, O'Connor plumps, reluctantly, for Livingstone. But never let it be said that O'Connor doesn't have at heart the practical, pragmatic issues most Londoners cherish, the stuff that should be meat and drink for whoever does become the city's mayor. Bendy buses, for instance; or, rather, the superiority of their predecessor, the Routemaster.

O'Connor is perhaps unique among the 10 candidates in having used one of the city's iconic red buses to escape the Metropolitan police when another Fathers 4 Justice stunt went pear-shaped, though you wouldn't necessarily put it past Johnson. “I have to admit he's done remarkably well,” O'Connor says, “but that's mainly because he hasn't done anything at all, he's just been completely sat on by his minders. Ken's the only credible candidate, really. And myself, obviously ...”

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