It’s a misty morning in March. I’ve got a stinking hangover and am being dragged round the block by the dog. Suddenly my friend Frank bounces out of the murk, part man, part Tigger. “Hey, Martin,” he says. “ I’ve had a great idea. Fancy cycling to my mum’s house?” Even by his zany standards this is bizarre. His mum only lives in Sydenham, about a mile from where we’re standing. “I mean, my mum’s house in Aix-en-Provence,” he adds. He’s half French, but is he half crazy, too? Aix is hundreds of miles away. But I know Frank and there is always a fearsome inevitability to his plans…

Three months later it’s another misty morning and Frank and I are about to cycle to his mum’s house. A vague feeling of disbelief grips me. Frank has persuaded two other misguided souls, Mark and Joan, to join us. The route Frank has plotted, from south London to the south of France, is a meandering 900-mile wiggle which will take us in a lazy curve across Kent and under the Channel before dropping the length of France. We’ll be cycling from La Manche to La Méd. To keep things interesting, Frank’s included un petit détour up and over Mont Ventoux – a windblasted 6,273ft mountain known as the Beast of Provence.

Over the months, our pleasant five-day jaunt has expanded into a full-blown nine-day adventure. There have been meetings (in the pub), training rides (1) and we’ve been assigned areas of responsibility. Frank: route planning, accommodation, kit, logistics, nutrition. Mark: extra route planning, communication. Joan: nothing. Me: nothing.

We finally set off at 7:30am on a Saturday in June for stage 1: London to Dover. Riding as a group takes some getting used to. Joan, a handsome Catalan adding some much-needed flair to our micro peloton, doesn’t seem to realise it’s not an actual race. He instantly disappears over the first hill. When we catch him he looks baffled at our lack of speed and stamina. “Where have you been?” he asks. I begin to worry our single training ride may have been ambitious…

Hours later we roll into Dover. Kent in high summer has been as pretty as ever, but this time it was pockmarked with Vote Leave banners. We board the Eurotunnel train and slip beneath the Channel, feeling relieved to be back in Europe, at least for a week. Frank’s sister lives in the tiny hamlet of Nortbécourt (pop 449), about 20 miles from Calais. She gives us a bed for the night and fortifies us with pizza and local cider – which we later discover comes from Hereford. We watch England scrape a toothless draw against Russia, marvelling at the antics of the hooligans in Marseille. Just other boys on tour, we joke.

Day two and our first proper taste of riding in France – and also of riding in heavy rain. Thank you, weather gods! We snake our way across the open pastures dotted with white cows, past old dairies and disused mines. “Where is everyone?” Mark asks. It’s a question we repeat over and over again in the coming days. Desolate roads skirt vast fields. We swoop through silent and shuttered villages as if we are the last people alive escaping a zombie apocalypse. The only signs of life are chained dogs. Fences are strung with dead crows – literal scarecrows. They work. We’re scared.

Then it’s on across the flat fields of Flanders. Poppies flutter everywhere. Arras is on the horizon, the Somme beyond that. We stop at the war grave near Bancourt. It’s the final resting place of Frank’s great uncle, Arthur James Fisher, sixth victim of Manfred von Richthofen – the infamous Red Baron. Arthur was killed at 21. Manfred went on to claim another 74 hits before being shot down himself and dying from his wounds at the age of 25. Arthur’s grave lies on its own at the edge of the cemetery. We stand around it in the drizzle, lost for words… at their courage, at the dazzling brevity of their lives.

We pedal on across Picardy and eventually arrive in Laon. It boasts an incredible five-spired, 12th-century cathedral which sits on a giant rock. Looming out of the mist, it hardly seems real – more like a princess’s palace. We check into an Ibis before heading back into the town’s beautiful square. It, too, is totally deserted. We are the only diners in the only open restaurant. We toast each other with pastis, and marvel at the cathedral. It’s covered in carved animals – dogs, horses, cows, donkeys and chickens. Mark discovers France has yet to open its arms to vegetarians when his asparagus arrives wrapped in bacon.

The following day we leave the battlefields and head for Champagne-Ardennes. The endless, immaculate vineyards are mesmerising, as if all the green slopes have been neatly combed. Past Reims and en route for Troyes the gentle hills peter out. The horizon is broken only by a phalanx of wind turbines. Their long arms turn elegantly like synchronised swimmers. It’s hedgeless, treeless, limitless… How can France be so big? How can it be so empty? It feels like we’re in the Prairies. We crank out a steady rhythm along rapier- straight roads that are 5km long without a kink. “Who’d have though you’d miss a bend,” Mark says, before trailing off, mesmerised by scale of the vastness.

We eat, we joke, we follow the wheel in front. It’s amazing how the hours spiral by, our minds set free to unspool. We become obsessed with spotting birds of prey. And goats. And ornamental wheelbarrows.

Day four brings proper sideways rain and wind so strong it fells a tree. We have to carry our bikes across it, Tarzan-style. It gives me a chance to practise my French. I flag down a motorist to warn her that: “Il y a un grand arbre à la route!” Mark tops this later by telling a pharmacist he needs decongestants: “Mon nez est fermé!” Frank, totally fluent, thinks it’s funnier not to help out at all.

Another day, another hotel, motel, campsite… they begin to blur. We try to remember what we’ve seen on which day. We start to get into a steady routine. Each morning we load up on croissants and coffee. Then there’s map chat. Then the creaming starts… Ride a bike for more than a day and everyone asks you about the state of your arse. Its wellbeing becomes a matter of intense scrutiny. We’ve brought bumper tubs of chamois cream and shovel handfuls of it down our shorts. It’s cool and soothing. We soon work out it’s best to do that after we’ve eaten the croissants…

By now we are two-thirds of the way down the country, we’ve inched past Bourg-en-Bresse, skirted Lyons and traversed the Drôme. At last La Belle France is beginning to live up to her billing. Provence brings us oak-covered hills, farmhouses, cherry orchards and fields of lavender.

But up ahead we know we still have our biggest challenge… an ascent of Mont Ventoux – a massive, brooding presence that dominates the area. It’s also a cycling mecca and this year the Tour de France headed to its summit on Bastille Day. (Well, it tried to – strong winds resulted in the summit finish being moved down the mountain and the race resulted in the bizarre sight of Chris Froome, the race leader, running up the road.) On the day we arrive the lower slopes are busy with cyclists rather than fans and everywhere we look Lycra-clad pilgrims are beetling their way up its vertiginous flanks.

It’s a 22km slog up an 8% incline. Near the top the trees give way and you arrive in a waterless, lunar wasteland. The camaraderie among the riders is amazing – shouts of “Allez” and “Courage” keep us straining ever upwards. It’s an agonising, lung-popping, thigh-burning two hours. At the top there’s laughter and backslapping and a glorious feeling of awe. We take in the view for a moment before turning and speeding to the bottom like stones dropped down a well – 6,000ft in 20 minutes. I find it terrifying and arrive at the end a jibbering wreck. Joan looks at his speedo and is disappointed to see he’s only hit 83kmh.

The final day takes us from Bédoin to Aix. We detour through Gorges de la Nesque, a spectacular limestone valley, and finally roll up to Frank’s mum’s house on Saturday evening: eight days and 900-odd miles after leaving London. We had one puncture (me), one fall (me) and one argument (me). The bike computer tells us we’ve burned calories equivalent to 17 pints of beer a day. So we head into Aix to put that right, starting with a bottle of champagne at Les Deux Garçons, the bar where Picasso and Cézanne also used to recharge their batteries. In keeping with the Tour, winners’ jerseys are awarded – for climbing and sprinting, but also for the most pee stops, rudest jokes and for the king of kit faffing…

After a week of perpetual motion, our wheels endlessly spinning, it’s so odd to come to a standstill. None of us can believe our journey is over. We look at each other across our champagne coupes. “Well,” says Mark, “my mum’s house is in Wales…”

Martin and friends were riding to raise money for the UN’s refugee charity. If you would like to donate, please go to Just Giving