LIKE COUNTLESS films which end with a scene on a deserted shore, this journey along the Thames has its eastern limit at the Maplin Sands on the Essex coast. But there is no final resolution here, only uncertainty.

The estuary may or may not extend this far. Marine charts show the sand banks and shoals deposited in its wide mouth and, taking these into account, draw the estuary's far boundary at the Kentish Knock buoy. Trinity House gives the buoy's location as latitude 51° 38’.085N., longitude 001° 40’.429E. This is several miles further east than Margate. The buoy once had a wave-activated whistle but this stopped working a few years ago.

Or perhaps it goes only as far as a line drawn northwards from the mouth of the Swale, like a cheesewire lopping the water into two bits marked 'sea' and 'estuary'. Close by is the old boundary to the jurisdiction of the City of London marked by two obelisks on each shore. One is in Southend-on-Sea, the other stands at an isolated spot by the Yantlet Creek on the Isle of Grain.

Boundaries and jurisdictions affect the Maplin Sands. Nearly all the land close by is controlled by the Ministry of Defence's oddly-named offshoot QinetiQ. Maybe the prominent Qs are a nod towards James Bond's inventive armourer for this is where, according to their website, weapons are developed and tested by firing, shaking, rattling, rolling, dropping, heating and freezing equipment and munitions.

The testing ranges must be noisy places if you could get near them, which you can't. Residents are kept informed of the sounds which can be heard from further away: for the 20th of January 2016 the site says that gunfire and explosions may be noticed – such notices are always may and not will. You can usually get to the shore across MoD land from Great Wakering on Sundays and sometimes on Saturdays. Signs forbid by law the taking of photographs on the attractively-overgrown land. This ceases to apply once you reach the shore and a causeway from the Wakering Stairs leads down onto the Maplin Sands.

Their expanse is vast at low tide. The causeway only goes out a short distance and from there on a public right of way called the Broomway extends across the Maplin Sands before rejoining the land six miles to the north on the island of Foulness. Like old earthworks which are only visible from the air, maps make the existence of the Broomway seem clear and definite. Here is an extract from an early 20th-century Ordnance Survey map, reproduced under Creative Commons from the Vision of Britain website:

Old Ordnance Survey map extract depicting part of the Essex Coast along the Thames estuary.

At ground level (or sea level) the Broomway exists more as an idea. It gets its name from the sticks and bundles of twigs once thrust into the sand as waypoints. Little more than stumps remain. Doubt fills the mind as you reach one and then scan the distance for the next. A black shape on the horizon looks like a possibility until it begins to move: a wading bird in silhouette. My nerve failed me after around five hundred yards and I went no further into the desert of worm-casts and puddles. A deep quiet hum came from unseen container ships or the docks on the Isle of Sheppey. Seabirds cried out, a bleak and compelling sound. The sand popped faintly as it dried in the sun.

It is easy to become disoriented out here. The mist descends, the tide rushes in quickly and people have occasionally drowned. Patrick Arnold's booklet The Broomway counted 66 such deaths in local parish registers over the years. The Broomway was the only means of getting on and off Foulness until the building of a bridge in 1922, so its use couldn't be avoided. It is also very old, but no-one is sure how old. One source suggests a thousand years, others are more ambitious and push the Broomway's origins back to Roman times, citing the vague authority of 'it is said'. It appears on John Norden's map of 1594 but isn't named:

Part of John Norden's map of 1594 depicting part of the Essex Coast along the Thames estuary.

One theory for the Broomway's existence is suggested by Debby Banham and Rosamond Faith in their recent book Anglo-Saxon Farms and Farming. They speculate that the Broomway began as a coastal drove road, the marginal position of which avoided the problems of leading cattle across other people's land. Since those times the coast has been eroded, perhaps catastrophically during the great storm surges of the 14th century, and so the Broomway is now semi-submerged.

Guided walks along the Broomway are run in the warmer months of the year by Nature Break Wildlife Cruises in Essex. The cost is £12 a head.

IntroductionChelsea HarbourMouth of the WestbourneCustom House StairsJane Parker, WappingNicola White, GreenwichThe Albert BasinRainham, EssexAveley Marshes, EssexProcter & Gamble, ThurrockPeter Beckenham, SwanscombeTilbury DocksShornemead Fort, KentCoryton Refinery, EssexAllhallows Marshes, Kent • Maplin Sands, Essex