The M25 precisely marks the northernmost edge of the London borough of Enfield. The motorway and all points south are in London, which is where we find postcode districts EN1 to EN5. I've been to all of those. Meanwhile everything to the north of the M25 is in Hertfordshire, which is where we find EN6 to EN8 (plus EN9 in Essex).
But the postcode district boundaries are a tad more approximate because they were drawn long before the motorway was driven through. My quest today is therefore to work out if any bits of EN6, 7, 8 and 9 dribble into Greater London, and if so to visit them.
The Ridgeway is a magnificent rural road, unsurprisingly along a ridgetop, running four miles from Enfield town centre to the edge of Potters Bar. The land to either side undulates with wide open fields and paddocks enjoying long distance views across valleys carved by tiny streams, and every time I come up here I'm amazed this is part of our global city. Almost all the addresses along The Ridgeway are in EN2 apart from those in the last half mile - essentially everything after the pylons. But Hertfordshire doesn't start until the last quarter mile, meaning a very short stretch manages to be in both EN6 and Greater London. It's pretty isolated and I think contains just four addresses.
• 501 The Ridgeway is a big twin-gabled detached house with a sturdy front fence and gates. This is just as well because a mastiff and a retriever appear should anyone walk past, which I guess is rare, and bark a lot until you go away. The owners have planted a shrubbery and a fir tree directly in front of their front door for maximum privacy, and also affixed a Jehovah's Witness logo to the fence for maximum publicity.
• St John's Prep School is the junior part of the main Senior School up the road. That's in EN2 but this is in EN6, its top notch facilities shielded up a long drive behind another set of gates. Nobody here sneaks down to the chicken shop at lunchtime, partly because lunches come free with your £12000pa fees but mainly because there are no shops of any kind anywhere near.
• New Cottage Farm is tucked behind the prep school and accessed up another drive behind yet more gates. From what I can tell it's more a 'diggers for groundworks' yard than an agricultural hub. It's also what the local bus stop is named after, indeed this is the northernmost bus stop in the whole of Greater London which is the only reason I'd ever been here before. I'm willing to bet you haven't.
• Botany Bay Water Tower was converted to residential use twenty years back, because who wouldn't want to live in a four-bed brick turret with a roof terrace offering commanding views. It's looking less lived-in at present, however, as if building works got so far and the cash ran out, so that's one less address to deliver post to.
According to various postcode maps EN7 crosses the M25 to encircle Capel Manor. This environmental college campus is a top place to study if you're the outdoorsy type, or to visit if you like wandering around the handiwork of horticultural students. As well as the show gardens they also have a little zoo, a cafe and one of London's largest hedge mazes, should you ever fancy a genteel green day out. But Capel Manor's postcode is EN1 4RQ and no constituent part or adjacent building appears to have an EN7 address in which case I don't need to visit this one, EN7's not in London.
This one's a relatively big overlap, EN-wise, in that it consists of eight streets rather than isolated outliers. Once again we're on the northern edge of Enfield, this time very nearly in Waltham Cross, along a thin strip of land once occupied by greenhouses. Bullsmoor Lane was then a minor lane and the houses built along it were designated EN1, but when infill started on the land behind this was appointed to EN8 instead. Here we find interwar pebbledash semis, postwar townhouses and lowly flats arrayed along minor roads and cul-de-sacs making the most of the narrow site. But it's the stripe of green facing Holmesdale that's the chief point of interest because this is the roof of a motorway tunnel and the M25 runs directly underneath.
The Holmesdale Tunnel was dug in 1983, a deep trench covered by a 670m-long concrete slab, acting both as an underpass and as part of junction 25. At the time it was the most expensive stretch of road in Britain, not that £30m would buy you much today, not even all the houses on the adjacent estate. The tunnel takes some looking after, hence the bunker-like control room at one end of Holmesdale and the substation at the other, both unseen by passing traffic. I wrote a full post about the Holmesdale Tunnel a few years back so you should go and read that if you want to know more. I'm not sure I'd want to live alongside this Ballardian mirage, but how fortunate that this narrow gap existed between London and Hertfordshire allowing the M25 to be squeezed through.
Only onehouse manages to be both in Greater London and in EN9 and it's a lockkeeper's cottage. It sits alongside Rammey Marsh Lock, the first lock south of Waltham Abbey on the Lee Navigation, and still feels like it's in the middle of nowhere. If the county boundary ran down the main river the cottage would be in Essex but instead the divide runs down the parallel flood channel so it lies marginally in London. Road access is over a humped bridge and along a pitted waterside track, which crucially comes in from the north so postal-wise the cottage is part of EN9 rather than EN3. And not very far along that pitted track the M25 goes swooshing over the river on concrete pillars, indeed this is the magic triple point where Greater London meets Hertfordshire meets Essex.
The lock was rebuilt in 1864 and if you look immediately beneath the bridge you'll see several blocks of Portland stone from the actual Old Westminster Bridge which had just been demolished. Alas the lockkeeper's cottage has also been rebuilt and in 1973 become a rather ordinarier bungalow, complete with attic rooms, PVC windows and Homebase lanterns. It's not the only property in EN9 1AL however, the tally also includes the Rammey Marsh Cruising Club, several moored houseboats and a cafe that I think now survives only in defunct advertising. It looked to me like some kind of community now exists on the cafe site behind chained gates but I didn't get too close because occupants were passing through, and because it was chucking it down with rain and I was a very long way from shelter.
In conclusion yes, EN6, EN8 and EN9 all sneak into London and no, EN7 does not. So if you've ever wondered whether or not you've been to all the postcode districts in London, unless you've been to New Cottage Farm and Rammey Marsh Lock no, you have not.