Travel: The secrets of the Thames archipelago

Only after a closer look do you realise how many there are. Two Tree, New England, Foulness, Deadmans and nine other islands fitted like loose jigsaw pieces to a coastal map. Although some barely fit the definition of an island, severed only by a narrow creek you could almost leap across, together they make up an often overlooked archipelago in and around the Thames Estuary.

Isle of Sheppey

It's odd that such a majestic boulevard should lead to Sheppey, the largest of the islands, when in the eyes of most mainlanders the island is a bleak appendage off the north Kent coast. Such gloomy opinions seem justified at first as you cross the Kingsferry Bridge over the Swale to be greeted by a featureless fried egg of an island with seemingly little to offer but a thin scattering of sheep and farm buildings. Many of those who have travelled this wide, tree-lined road have done so either en route to the Dutch town of Vlissingham via the port of Sheerness (now no longer an existing crossing), or at Her Majesty's pleasure to one of three prisons on the island. Curiously most of the weekend traffic queueing on to the island headed for neither, turning instead for Leysdown on Sea, out of sight at the eastern end of the island.

Too small for a town, Leysdown is a resort, a low-rise, low-cost, flip- flop kind of place with a sandy beach and a character of its own. Leysdown has been a traditional seaside retreat for south and east Londoners for over half a century. Lil's Eels serves a friendly pie `n' mash, the Crest Club has an "audience participation cockney pride show", while at the Seahorse pub they serve up a heady cocktail of all-day drinking, all-day breakfast and all-day karaoke. While it might be easy to sneer at Leysdown, the real attraction is the clean sandy beach and a friendly community of chalet and caravan parks whose owners return religiously to this home from home.

I took a walk through acres of wooden chalets, past No 77 Sunset Strip, the Holiday Inn, Den and Carol's Place and the Tudor Nest. Each decorated and adorned to the owner's taste. Some plain and peeling, others freshly painted, pink, green with ruche blinds or a weather vain. One had Disney murals, another with a celebratory "Spurs 2-1" daubed all over the side. There's no Habitat conformity here.

This liberated attitude took a different shape further east along the coast as Leysdown disappeared into the waist-high seagrass that marks the start of the official naturist beach. There's little warning - visitors straying too far along the beach in search of the quieter parts of the island find themselves on unfamiliar territory among the fat, hairy old men who inhabit this stretch of the coast. Distractions aside I headed for Shell Ness at the eastern tip of the island. The beach at Shell Ness, not surprisingly, is made entirely of shells. It feels almost too delicate to walk on, every footstep crunching the beach to a finer dust that glowed white in the afternoon sun. Like every visitor to Shell Ness I filled my pockets with shells and walked down to the water's edge to stare across the Swale to Whitstable and Seasalter on the mainland. It's here on this lonely beach that Sheppey really does feel like an island.

Shell Ness marks the end of Sheppey proper. Carry on along a path of white powder and you reach the RSPB reserve on the marshy ground that covers the southern half of the island. Although Sheppey appears to be one island, the marshes comprise four other islands: Elmley, Harty, Fowley and Deadmans, the latter two small and inacessible with Elmely and Harty making up much of the featureless side of the island that greets you as you cross the Kingsferry Bridge. Places of interest are the bird reserves on Elmley and Spitend marshes and St Thomas's, a 900-year-old Norman Church that stands alone on Harty Marsh.

Those who turn left on arrival to Sheppey head for Sheerness. What little tourist trade Sheppey's principal town once enjoyed dried up at the end of last year as the last passenger ferry made its crossing between the island and the Dutch mainland at Vlissingham. Now, only freight cargo makes the crossing over to Ostend.

But if the town has anything of interest today it is the activity of the working port itself and Blue Town, the old dockyard quarter so called because the dockers stole Navy issue paint to decorate their houses.

Foulness, Wallasea and the eastern Essex cluster

Shells of the exploding kind are scattered all across Foulness, the largest of this group that sit between the mouth of the Thames and the River Crouch. You'll need permission to visit Foulness and its smaller neighbours Potton, New England, Havengore and Rushley where, for the last 150 years, they have been part of a weapons testing site. Curiously a group of rare and presumably deaf avocets (the RSPB emblem) have chosen to settle among the military debris on a part of Foulness that has become a Site of Special Scientific Interest. Despite the obvious dangers of living in such a place there has been a small human community with a pub and a church on Foulness for generations. You have to get permission to visit them, too.

The only other island in this cluster with signs of life on the map is Wallasea, which has a marina. There are three reasons to visit this marshy island. First, if you have a boat, secondly, to meet the captain of the Lady Essex II who for a fiver will take you out into the estuary to see the seals, and third, to visit Grump Jacks, a popular bikers' haunt and "roadies museum, dedicated to life on the road". It's the creation of an ex-trucker who toured Europe with all the big rock bands gathering a collection of personal memorabilia which now furnish the walls. Other alluring features include "free grub to bikers, free drinks for outrageously dressed [or undressed] females, and a free campsite to crash in".

Canvey Island

Perhaps the most well-known of the islands is Canvey which sits wedged into the south Essex coast. Visually, very little seems to separate Canvey from the Essex mainland, but stay long enough to poke about the island and you can find what does set it apart.

The answer lies in Canvey's coat of arms which features a tiny, round, thatched cottage and whose motto reads: "From the sea by the grace of God." It is a reminder of the island's continual battle with the water, except it wasn't divine intervention that saved the island but the commissioning of a Dutch engineer to reclaim and protect land lost during a long period when Canvey was being engulfed by the sea at a rate of a foot a year. As payment for the work Dutch labourers were given a third of the reclaimed land to set up home. Consequently the Dutch legacy pops up all over the island as surnames, street names and tiny thatched cottages, of which only two remain dating from about 1610. One has become the Dutch museum. It's a tribute to the Dutch without whom Canvey Island might have become the Bay of Benfleet.

Isle of Grain

With no bridge or ferry crossing, you arrive on the Isle of Grain wondering at what point you left the mainland. A waterlogged ditch does suggest some form of divide but it is no longer possible to circumnavigate the island. Grain ceased to be an island proper years ago when the Yantlet Waterway naturally filled with silt, bridging the divide between the island and north Kent. Little is recorded of the island's early history, which is unfortunate as in the Seventies the mothership of all power stations landed, smothering what little there was. A walk around the periphery of Europe's largest oil-fired power station provides a few clues to what was once here. Black stumps at the end of Port Victoria Road are all that remain of the hotel and pier where royalty once embarked. In the shadow of the power station a 19th-century fortification crumbles and across the muddy foreshore sits Grain Tower, a derelict fortification. One can only wonder how different the Isle of Grain might have become had Port Victoria thrived and the power station not been built. But to walk along these lonely fringes with arrows of Brent Geese overhead and distant horn blasts drifting in from the shipping lanes you do feel a sense of detachment even if Grain is now attached. This, for me, is reason enough to keep calling it an island.