Underground London by Stephen Smith

As London has aged mightily and grown exponentially, so its capacity to both enchant and inspire has grown into a full-blown subject. London is no longer merely a muse for artists and writers, or a fruitful little patch for the peregrinations of amateur topographers, but an object of study comparable to organic life itself. Stephen Smith certainly ends up agreeing with this lofty view; after performing numerous biopsies on the urban corpus, he quotes Richard Trench approvingly: "Like the human body, London hides its organisms within it. Their arteries bearing the body's fluids, lungs enabling it to breathe, bones giving it support, muscles endowing it with strength, nerves carrying signals, and bowels disposing wastes."

The British Psychogeographers, with Peter Ackroyd and Iain Sinclair in their van, have taken the phenomenon of London as their starting point. By scraping away the verdigris from the city's nameplates, and the moss from its stones, they expose its phrenological bumps and mystic currents of psychic force. Smith has now dived beneath the Great Wen to discover the taproot of this monstrously warty excrescence of urbanity, and what a rich trove of subterranean delights he has brought to the surface.

However, unlike his fellow London academicians, Smith is neither a perverse polymath nor a hobo hierophant. Instead, his style is breezy and inclusive; he takes his readers by the hand and drags us gently down into the pays bas. The motive for this tour beneath the city streets was Smith's own sense of claustrophobia travelling on the Tube after a time away. So, meeting first with the northern miners digging tunnels for London's galvanic nerves, he proceeds to the city's bowels - the great sewer system - where the "flushers" kit him out and take him shit-dabbling. On Smith goes to London's now-buried rivers - the Fleet, the Walbrook et al - before indulging in an archeological investigation of the muscular foundations of its built environment.

Like a knowledgeable nematode, Smith is never happier than when boring his way through London. He's an affable companion, able to ingratiate himself with lone foot patrollers of the Tube and eccentric custodians of buried south-London monasteries. Only the anoraks of "Subterranea Britannica", a claque of nerdish fellow nematodes, remain impervious to his charm. The sheer range of the information he digs up is startling, and while his ostensible subject is the ground beneath our feet, he ends up writing a fairly comprehensive history of the city from this lowly perspective. Thus he reads the city through its historical layers, delineating the Roman beneath the Saxon, descrying the Saxon beneath the medieval, limning the medieval beneath the Tudor.

The astonishing 12th-century "Great Conduit", which ran from Tyburn (Marble Arch) to the City, is exposed to our view, a water main built from elm trunks with lead quills running off to the houses of the rich. Smith also gains access to vast, Victorian Honor Oak Reservoir, where 60 million gallons slosh about in the middle of a golf course. He breaks into the "dreary stuff-ness" of the Silver Vaults beneath High Holborn, and joins modern tomb-robbers as they clear the plague-infested vaults of a church. He dives under Parliament and examines the sewage ejectors that labour to process the ordure of our legislators, and breaks into the featureless façades of Whitehall to show the tunnels between the secret "Cobra" operations room, where the Iraq War was planned, and an immured Tudor real-tennis court.

For the reader who likes their underground London spooky and secret, Smith's evocation of the huge complex of government tunnels is exemplary. I will never be able to visit the gents toilet at the ICA again without being acutely aware than I'm micturating alongside a mysterious portal that plunges down 100 feet to where 25 miles of Cold War bunkers link five massive "citadels". This is truly the icy state berg of which Tony Blair's wannabe cool is only the visible eighth.

Stanislav Lem, the great Polish writer, penned a Kafkaesque novel, Memoirs Found in a Bathtub, in which the Pentagon descends beneath the surface of Washington to escape a Soviet strike. Stephen Smith's perspicacious potholing shows us that our titular lords and masters, like the rats we know them to be, have already prepared their boltholes.

Will Self's 'Dr Mukti and other tales of woe' is published by Bloomsbury