David Pott woke up one morning in 1997 possessed of the image of a snake wrapped around a stick. He wasn’t at all sure quite what it meant. “Why had God given me this vision?” he wondered — and, luckily, before the day was out, God had nudged him in the right direction.

“The stick resolved itself into the Greenwich meridian,” he explained, by the bank of the Lee navigation canal, just beyond the M25, on a cold and crisp afternoon.

“And the snake?” I ask, as we traipse along the towpath.

“That was us. Walking along the meridian, snaking in and out, crossing the line every few miles.”

And so it came to pass that the Lifeline Expedition was born, an organisation founded to foster reconciliation over the vexed issue of slavery. David has been walking ever since; up and down the US, across Africa and, most recently, the 200 miles from Hull to Greenwich — one mile for every year since the slave trade was abolished. He is a very fit man by now, for a 60-year-old. All that walking.

They’ve got their timing right, of course. David Pott’s little troupe is merely a tiny part of this weekend’s antislavery commemorations: today, in London, there will be more people saying sorry to one another than at a national convention of inveterate apologists. You see, it is the 200th anniversary of Britain’s commendably early decision to abolish the traffic in slaves across the Empire — and over the next 30 years all slaves held by British companies and individuals were freed.

Of the western European super-powers of the time we were not perhaps the worst offenders — that would be, by some considerable margin, Por-tugal. Nor did we invent slavery — the Africans themselves had been enslaving one another for century after century before we came along and, indeed, in some cases continue with the practice today.

And there were the Arabs before them. Not to mention the Romans, of course. But just lately we have become extremely apologetic about the whole business. The prime minister has made a statement of regret and apology for our comparatively brief but lucrative involvement; John Pres-cott has apparently decided there will now be an annual commemoration day. And some of the African countries, forgetting their own complicity in the slave trade, have been demanding more than mere humility from the West — they want reparative dosh, lots of it, now.

Some $777 trillion, according to the last African convention on the issue. That’s something like 10 times the world’s annual GDP. And if the British public hasn’t quite taken the issue to its collective bosom, here are still one or two chaps like David carrying the banner.

He’s got some followers with him, a gaggle of 13 like-minded souls, most of whom are wearing T-shirts saying “So Sorry”. If they meet any descendants of slaves they are apt to fling themselves on their knees and beg for forgiveness. As a reporter, I would quite like to witness this sort of event. But there aren’t any descendants of slaves in Broxbourne today, down by the river. Just some bemused Canada geese. No point saying sorry to them.

Not all of David’s followers have walked the entire length from Hull; only two of them have done that, in fact — a likable 15-year-old American boy called Jacob Leinau, who was apparently told to put on his hiking boots by both his dad and God, and a lady called Monette, who hails from Martinique and carries the big stick with the snake on it. The rest just joined in as they hit Hertfordshire.

To symbolise the plight of the slaves, David and Jacob are linked together by a crude wooden yoke. When they clamber over fences or down ditches they take the yoke off for very sensible health and safety reasons. One or two of the others are linked by heavy steel chains.

David is, as you may have guessed by now, a fervent Christian — as are the rest of the marchers. Before he started walking he was a teacher in independent schools. “Then,” he says, “I began to get involved in reconciliation issues.” Now he gets by with, as he puts it, “doing a little bed and breakfast” and through charitable donations and gifts, such as the £2,500 they got from Lewisham council. Good old Lewisham.

Reconciliation issues: it’s not just about slavery. David has also walked the length of Offa’s Dyke — which wasn’t, as you might suppose, simply an agreeable hike in the delightful Herefordshire countryside. “That was to foster reconciliation between English and Welsh people,” he says.

“Um — do they need much in the way of reconciliation, then?” I ask him.

“You’d be surprised,” David replies. And then I have to be quiet because the next mile of the walk is to be undertaken in silence and contemplation, at David’s sudden suggestion.

Later we stop at a monument bang on the meridian, near Waltham Abbey in Essex, and, after David’s said some stuff about the meridian linking countries that traded in slaves and those that provided them, we gather around the obelisk to pray. After a while, the lady from Martinique with the stick, Monette, begins to keen and wail in a most distressing manner. David puts a brotherly arm around her while some of the rest of us stare fixedly at our feet.

“What’s up with her?” I ask, when the keening has stopped several minutes later.

“That sort of thing can happen from time to time,” David quietly explains. “People feel so connected to this issue. Monette is traumatised by the fact that she has just learnt that the Bishop of Exeter was awarded £16,000 from the government to compensate him for the slaves he had to give up. She’s only just found that out. She thinks it is terribly unjust.”

“Oh. When did that happen?” “The 1830s,” he says, and we march ever onward, towards the abbey, where a prayer will be read out. The next stage of the walk will take them to Walthamstow, E17 — a place which, you might argue, could do with some form of lifeline, whether provided by David or anyone else for that matter. The last stage of the journey was due to be completed yesterday afternoon.

They’re an affable and sincere bunch, the marchers — and diverse, too. Quite apart from Monette and Jacob and his little sister, there’s Rob-erto Carlos Gonzalez, a “missionary” from Barranquilla, on the north Colombian coast. And there are some people from Tring. They’ve been joined, at various stages of the march, by a handful of local Christians, whom they have also relied upon for shelter overnight. The day before I met them they had cowered for hours in some kind soul’s garage as a blizzard raged outside.

David will most likely stay as fit as a fiddle. Once this march is over, he’s got another one planned. In the summer he’ll be taking his followers on a 437-mile march from London to Bristol and then all the way up to Liver-pool (they could use that old Offa’s Dyke route again). This is to link together the three great English ports that, it is generally agreed, owed their enormous affluence to the industrial exploitation of African slaves between 1500 and 1807.

And after that I dare say there will be more long marches to various symbolic places, the chance to say I’m so sorry to someone about something, and to get a little bit of fresh air.

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