Halfway through Europe's most glorious century, the 19th, Eugne Guinot opined "in Europe there are two capitals: Paris for the winter and Baden-Baden for the summer". This month I have visited both. However lovely the German spa town may be, it does not have the qualities of scale, diversity, wealth and culture that defines a great capital (and no, it wasn't just that I was there in the wrong season). The French capital has a stronger claim, yet it has been comprehensively out-pointed in our survey of civic greatness. London is the world's capital, and ex officio capital of Europe, the northern hemisphere and, let's speculate, the solar system.
To get a sense of the reality behind the numbers, take a cross-section through the ultimate global village starting at the antithesis of Heathrow: London City Airport. The Docklands airport is a small gateway to the capital that is a pleasure to use. It is also, thanks to the UK's openness in aviation, a battleground between British, Belgian and French airlines. And it is an excellent example of re-using the docks that enabled London to wrest, in the 19th century, the title of global capital from Amsterdam. Alone of the capitalistic capitals (New York, Tokyo, Frankfurt... ), London has a "downtown" airport that is within easy reach of the financial centre or, for the past decade or so, centres.
The skyscraping money factories of both the original City of London and the young pretender, Canary Wharf, decorate the skyline as you glide west aboard the Docklands Light Railway. This driverless train network is another exercise in reinvention, turning obsolete 19th-century railway workings into people-movers for the 21st century. On the south side of the Thames stands Greenwich, resplendent in its status as one of the four Unesco World Heritage Sites in the capital, and just upriver lies Deptford where Peter the Great, as an Imperial work-experience candidate, learned how to open Russia to the world.
Before you reach the Tower (another Unesco site), and the fragments of the Roman wall around the core of the city, descend to street level to wander through Whitechapel and Spitalfields. These areas were traditionally where minorities from Jews to Huguenots arrived from Europe in search of tolerance.
A good definition of a "Londoner" is "a person from somewhere else"; a better definition is "a tolerant person...". Londoners put up with a great deal in their daily lives, not least coping with a constricted capital that has not enjoyed the benefits of mass clearance of the metropolitan arteries (as Baron Haussmann did in Paris) or a tidy grid (which keeps Manhattan moving). Half-century-old buses stutter along streets laid down by the Romans nearly two millennia ago, while beneath the streets the world's original and most extensive Underground railway ticks along to its own eccentric clockwork.
What London lacks in transport facilities, it more than makes up for spiritually; Church of England worshippers with lofty aims can choose from St Paul's Cathedral, Westminster Abbey and Southwark Cathedral, which celebrates Shakespeare. Four hundred years ago the genius was part of the industry of human happiness based south of the river an ironic location, given the suffering on the south bank of the Thames. The "dark, Satanic mills" of Blake's "Jerusalem" were the flour mills of Lambeth, and in Victorian times, Dickens walked these streets to chronicle the dark side of London.
Now, the South Bank thrives once more thanks to innovations such as Tate Modern (the world's most successful art venue of the 21st century), a revitalised Festival Hall and the London Eye. Artistically, the Eye's magic circle complements perfectly the Westminster Tower (colloquially Big Ben), though the tourist flow between the two is impeded by Baghdad-style fortifications installed after the invasion of Iraq.
Visitor numbers to London were hardly dented by the murderous attacks on the Tube in 2005 and are holding up well despite the weak dollar. Some deft 19th-century purloining of treasures from abroad have bestowed London with magnificent museum collections, while 21st-century no-frills airlines import millions of travellers from the continent to Europe's most alluring or, at least, easiest-to-reach city.
Easy to reach, difficult to comprehend: to see how much more there is to fathom, wander down the basement of Stanfords, the map and travel guide shop in Covent Garden (and venue for some of our researches). You can walk across the full extent of the city in about 10 seconds flat, because a giant map of the capital is printed on the floor. The anarchic patchwork is the result of two millennia of settlement, centuries of political and ecclesiastical intrigue, an anachronistic monarchy and episodes of city planning varying from inspired to risible. In its glorious muddle, London comprises all that is good, bad and plain daft about humanity. For all its flaws, it remains Britain's window on the world and the most successful city on the planet.