I'm not sure I fully understand the term "psychogeography". To me, it means the exploration of an unlikely place or a hidden aspect of a place, and whenever I hear it I think of Sunday walks in my childhood, when we would follow an overgrown and neglected path and sometimes scrape away the turf to discover a square stone with bolt holes drilled through it. As beetles hurried this way and that across its surface, my older brother would explain that the stone had once held an iron rail and that the path had once been a wagon-way, built in the 18th century to take coal from the Fife pits to a harbour on the Forth.As nobody else seemed to know or care about these facts, I felt I was sharing a historical secret. There were several of them close by: dark, deep ponds that had once been quarries; a ruined slipway built to take seaplanes; steel rings that had tethered barrage balloons; an abandoned railway tunnel where bats flew. Like a great many people in what was at that time an industrial country, I grew up in a landscape that was interestingly pockmarked with successive eras of exploitation, and all of it so commonplace that beyond a mention of its origins, Watt's engine or Crompton's spinning mule, it never found a place in the history books.

Almost all of that Fife landscape has now been buried without ceremony by motorways and housing estates, but equivalents can be found elsewhere, none of them grander and stranger than that part of Kent known as the Hoo peninsula, which lies between the Medway and the Thames and which, if Norman Foster and Boris Johnson have their way, could become the most vital stretch of land in Britain. As the location of Foster's proposed Thames Hub, the Hoo peninsula will be paved with new railways and docks and the four-runway airport with which Johnson wants to replace overcrowded Heathrow. A new Thames barrier will generate electricity from the currents and tide. Passengers who land there will take ongoing flights and containers ongoing trains.

The scheme is so ambitious – Foster says it requires us "to recapture the foresight and political courage of our 19th-century forebears" – that estimating the cost beyond dozens of billions is pointless. Nevertheless, David Cameron has included it among the options to be considered when the government decides how the UK can continue to provide a hub airport for Europe: pledges to the voters of west London having ruled out Heathrow's expansion.

If Hoo were chosen, which isn't unlikely, the question then becomes: what would be destroyed to make way for it? The Royal Society for the Protection of Birds has, as usual, the quickest and simplest answer – the wetland habitats of visiting species – but beyond that the losses are less definable, and not so easy to raise a fuss over. Since Dickens's day, the creeks and marshes of Hoo have had a bleak form of celebrity as the spot where Pip first met Magwitch, and where prison hulks (Magwitch had just escaped from one of them) could be occasionally glimpsed through the mist on the Medway. In fact, the countryside is prettier and hillier than you expect. On a hot day last week, workers from Poland and Bulgaria were spreading straw across fields of strawberries while the knapped flint of Hoo's several 13th-century churches shone in the sun. There is also a 14th-century castle owned by Jools Holland and a workaday marina, about as far from Cowes in its social atmosphere as it's possible to get.

The main impression is of tremendous utility. Power lines sag west towards London to take electricity from the power stations at Kingsnorth and Grain, whose chimneys stand solid against the sky. A diesel rumbles along a single-track freight line with a train of containers from the dock near the peninsula's tip. And beside this present activity lies the evidence of older industries come and gone. A good guide will point out the hollows in the tidal reaches that were dug out in the 19th century when Medway mud was loaded into sailing barges by labourers called "muddies", taken to kilns and mixed with chalk to provide the London building boom with cement. What he needn't point out are the barges, which rot as nicely shaped timbers where the highest tide has left them and are in their way picturesque.

This is also a place of blighted ambition. The railway, for instance, was built for a glamorous purpose it only briefly fulfilled. Trains would take cross-Channel passengers to a pier with a hotel attached called Port Victoria, where they could catch steamers to Belgium and cut a few minutes from journey times offered by rival companies. But only Victoria, the monarch, found much use for it and long before the second world war the Hoo line had become a little-used byway. It last saw a passenger 50 years ago. Port Victoria has been buried under oil pipelines and mud.

Then on Hoo's northerly coast, there is Allhallows-on-Sea, the Ozymandias of seaside resorts. Developed by the Southern Railway, which built a branch to it in the 1930s, Allhallows was intended to have 5,000 houses, several hotels, a zoo and Britain's largest swimming pool with a wave-making machine. Then the war intervened. Postwar Londoners failed to return as holidaymakers and the railway closed. Today a big, echoing 1930s pub, the British Pilot, stands at the end of a cul-de-sac, beyond which is a park of holiday chalets and a sea wall with views across the estuary to Southend. Retired couples spend their summers there and winters in Goa or Cyprus, dividing the money released by the sale of their old homes between a chalet in Allhallows and a flat in the sun. "We don't do cold," says a tanned woman in her 60s, talking of these annual switches; while another wonders what will happen if her husband dies before her and she, a non-driver, is left alone in this inaccessible place.

Would it matter to the world beyond, other than to birds and ornithologists too, if Hoo became a giant airport and dock, clustered with warehouses, freight yards and car parks? It looks no more than a fitting next step for a peninsula that has for centuries been so ruthlessly used. Really, unless you live there, would you care?

And yet something important will go: wreckage, the traces of a previous era that have no official curator and are therefore delightful to find. High up one of Hoo's creeks sits a motorised barge, built in 1915 and long defunct, but still cared for by her last skipper, Cliff Pace, who turns the pages of his old logbook smiling at what he and his barge once achieved. "We took 3,237 bags of prunes from Albert Dock to Whitstable … 5,385 cartons of corned beef from the Victoria Dock to Stroud … 163 bundles of pick-axe handles from West India Dock to Otterham Quay." Even in the 1970s, the estuary was busy with lighters and lightermen – lovely times, says Mr Pace, but all gone. I look at his entries in the logbook and feel, just for a second, the same sensation of discovery that came when a carpet of moss was peeled from a square stone, the beetles scattered and my brother said, "Look…"