If you don't have a car and are coming from elsewhere in London, the obvious place to start this walk is ChessingtonSouth station. Trains go no further, even though the tracks do, this being as far as the railway had (just) reached when WW2 started. Green Belt legislation then prevented further suburbanisation in the fields beyond, so the extension to Leatherhead was never completed, and the rural landscape you're about to explore is the happy consequence.
You're looking for Barwell Lane, just past the Business Park, on the other side of the busy Leatherhead Road. Barwell Lane is anything but busy, being a cul-de-sac frequented mostly by people who like horses, and which boasts a Pressure Reducing Station partway along its length. The first proper footpath begins beside an overgrown sign warning those who venture further that Animal Behaviour Is Unpredictable, which isn't necessarily what you want to hear this close to a safari park.
Chessington's savannah simulation Ride into Africa! is barely 100 metres away, behind a row of trees which perfectly conceal participating giraffes, white rhinos and zebras. Instead the only beasts you're likely to meet are grazing horses, as the path rises up to an open paddock on the flat summit of WineyHill. All the usual comments about being able to see the City and Docklands on the skyline apply (although a plaque which ought to explain which building's which has been untimely ripped).
The path continues to skirt Chessington Worldof Adventures, whose well-fortified rear fence becomes increasing apparent as you progress. I walked past yesterday when the park was closed, and silent, but the Tomb Blaster and Kobra rides immediately behind the fence are likely to be livelier today. Only those visitors who park their cars in Gorilla Field will ever see the last field in London, which rolls down to an unseen lake and the Esher Bypass before rising up to a scenic plateau on the Surrey side.
I've never before seen a sign marked Theme Park This Way on a waymarked walk, nor the entrance to a luxury glamping enclosure. I was wholly unimpressed by two No Pedestrians signs that Merlin Entertainments had erected on this peripheral public footpath, presumably with their car park visitors in mind, attempting to funnel them towards the park's back entrance. But most disturbing of all was a sign reading Welcome to the Leopard Field - an unfenced expanse of grass used for overflow parking, so thankfully home to nothing scarier than a Beetle or a Jaguar.
It's a pleasure to get away from the theme park environs, recrossing the busy Leatherhead Road to follow a half mile wooded path littered with snapped-off oak branches. You'll only find it quite this covered by acorns if you too walk through on the day of an autumn gale. What follows was my favourite part of the walk, across a vast open field that's gently valley-shaped, but flat enough that it was used an airstrip during WW1. The wonderfully-named Bonesgate Stream rises close by, and wiggles down to Rushett Lane within a tree-topped trench.
6♥ Beyond the field boundary might have been London but is actually Surrey, fractionally the borough of Epsom and Ewell. A coal tax post marks the divide (and there's another shortly afterwards, if you're a collector). This spot marks the northern edge of Ashtead Common, a sizeable nature reserve run by the bottomless pockets of the City of London. It looks well worth exploring, but the Chessington Countryside Walk merely skirts the woods and heads instead for the corner of Epsom Common.
Well this is all very pleasant. The forested paths emerge alongside the Stew Pond (where Stew is a ye olde word for 'fish'). A sign warns owners to keep their dogs out of the water, so this is of course where I encountered the most dogs on my walk, including two lively damp labradors and a very inquisitive boxer called Lola. Epsom Common's bridleways are one of the reasons that the CCW leaflet recommends "boots or stout footwear", indeed even in September several pre-mudbath stretches were already apparent all around the route.
Next up is Horton Country Park, formerly the site of the largest complex of psychiatric hospitals in Europe, now mostly paddocks. West Park Asylum has been reimagined as Noble Park, a vast private estate of desirable residences, its water tower still visible for miles around. The country park's logo promises green woodpeckers, but I saw only ponies and a squirrel... plus, ooh, a field of deer staring back at me inquisitively through the fence.
10♥ For the last mile it's back to London, reached by stepping through another gap where a stile used to be. Here is another huge field straddling the Bonesgate valley, the remains of its harvest already ploughed back in, and a phalanx of pylons stalking down the centre. The aforementioned stream now has more width, depth and flow, and requires a proper footbridge to cross, before the path reaches the backs of some back gardens, and hey we're back in Chessington proper.
The 12th century parish church sits at the top of equally medieval Green Lane, but you're not going that way, you're bypassing flats and catteries to follow one last footpath. This climbs a bit of a hill to look south across Chessington Golf Centre, and beyond that most of the undulating green landscape you've just orbited. It's a nice finale to try to pick out the route you've been following, before a few simple minutes lead you back to the station.
"Allow four hours" they said, but I did it in precisely two. A fine walk for cobweb-blowing, I'd say, and yet another to add to my Unbelievably This Is Outer London list.