London barely glanced as four bedraggled figures on dirty motorcycles made their way through bristling traffic.

It was a day we had been hoping to reach for nearly two-and-a-half years. It struck me, though, that for those honking horns at traffic lights, hurrying along crowded pavements and flagging down taxis, we were a grimy flash of colour soon passed: a curiosity - or unnoticed.

I have always thought of London as a city painted in watercolours. A slightly washed-out look permeates the streets. The dominant colour seems to be grey: damp concrete, overcast skies, stone buildings. Of course, vibrancy is there if you look for it: the deep red of a London bus, the striking greens of a London park, the bright orange writing of a corner kebab shop, and the shiny blue of the BMW-1200 that pulled up next to us as we struggled to find our way through the city's outskirts.

"I'm a reporter from Motorcycle News - where are you guys from? Need any help?"

As on so many occasions during our travels, help had appeared just as we needed it, and soon Gareth was graciously guiding us through London's twists and turns to our appointed destination, Trafalgar Square.

We passed history to rival many of the great cities we had seen, and also signs of more recent change - in one London district, for example, we saw more women clad in hijab and burka than in any of the Muslim countries we had ridden through.

We performed the last of several thousand illegal manoeuvres on our motorbikes, bumping our way over a central traffic island, before parking next to Nelson's Column, our view of Trafalgar Square obstructed by a large container that was temporarily residing in the square as part of some exhibition.

And that ... was it.

We had finished. Climo flopped down, spread-eagled on the ground, grinning with relief. I knelt down, feeling the cold stone slabs with my bare hands, touching the finish line, speechless, relieved.

Two years of planning, five months of riding, 27,000 kilometres, 19 countries; a broken leg, a sprained ankle, altitude sickness, diarrhoea, bee stings; broken wing mirrors, flat tires, major crashes and minor ones, dirty carburettors, engine bearings, wheel bearings, cracked frames; watching the sunset over a bottle of wine, early-morning solitary skinny-dips, Russian saunas, exhilarating swims, unfathomable mountains, summer meadows, scorching deserts, fiery gas craters, a dried-up sea; meals of unidentifiable lumps of fat, meals of partridge, salmon and chicken, meals of salami and dry bread; nights spent sleeping in the rain, in the snow, in the heat, under the stars, next to railway tracks, next to motorways, under cellphone towers, at the foot of glaciers, on the banks of gurgling streams, content and happy, cold and disconsolate; offers of hospitality from random strangers, shepherds, security bosses, former KGB agents, missionaries, mafioso, restaurant owners, nomads, drunks, ambassadors, church members, fellow adventurers, truck drivers, soldiers, scientists; moments of elation, despair, achievement, anger, brotherhood and pain: all this was over, as permanently and irrevocably finished as yesterday.

We milled around our bikes, grinning like awkward schoolboys, hugs and backslaps all round. Passers-by stopped to ogle briefly, some even pausing long enough to talk, take photos and offer their congratulations.

Inevitably, however, we were asked to move our bikes by a security guard - the fact that we had ridden across the world to get to this square was irrelevant.

After realising that our bikes were not welcome at any of the major tourist sites in central London, we made our way to a pub for a celebratory pint.

Our arrival at the pub did not attract as much attention as the misdemeanours of two drunks on the footpath outside: one pushed his way into a group of people, then squatted down to graffiti the pavement, before standing up, issuing an approving laugh, and running off down the road to spray his name over the walls of the local Starbucks cafe.

A second drunk ran up with a fire extinguisher, crying "I'll clean it up!" and spraying the contents of his bottle at the gathering crowd, before being flattened by a single punch from a man he had squirted.

After drawing large crowds throughout Asia, slapping hands with kids as if we were running the last victorious metres of a marathon, posing for photos and even occasionally signing autographs, we were now insignificant, less entertaining that a couple of cavorting clowns.

I was happy to leave it that way. I parked Piza in an old shed at the back of a friend's flat that night, finding her final resting place between bags of rubbish and old carpets. It would be the last time we rode together.

"Where you from, then?" asked an Irish guy that Saturday night, in another pub where we had reunited to reminisce about "the trip" (already referred to in the past tense).

When I replied "New Zealand", he asked "How'd you get here?"

"By motorbike," I said, satisfaction lining my voice.

After a lengthy pause, the man responded: "Well, there's a lot of water between here and New Zealand, isn't there, so all you really did was sit on a boat for ages, didn't you, you dirty, lazing, lying f***"

That weekend, I farewelled my three fellow riders, friends that had become more like brothers over the last six months, as we each went our separate way.

Misha and I were last to say goodbye, and then he faded into the dark, drizzly night, and I was alone, by myself for the first time in months, with nothing but my reflection dancing from puddle to street-lit puddle watching me.

As I turned and walked back to the nearest tube station, I had mixed emotions about the adventure just finished, but I knew exactly how I felt about the adventure yet to come.

Six months ago I was at Auckland Airport, forcing myself to walk away from the tearful embrace of my beautiful fiancee, knowing I would not see her for another six months (assuming I survived the trip).

Now, I was returning, ready to face the new adventure and challenges that marriage would bring. I had been across the world, seen staggering scenery, experienced a diverse range of cultures, faced difficult ordeals and met some incredible people, but I knew there was nowhere I would rather be than back home, with my girl, ready to tackle an even bigger, more exciting adventure that the one I had just completed.

* Rob and his mates have finished their epic journey from Vladivostok to London, but there will be more opportunities to read about their adventures, as Rob plans to publish a book on their experience. For more details, see the 51st Traverse website.