On Alderney, the Northern Line terminates at a lighthouse.
There is no soot-black tunnel, no stentorian voice announcing an approaching train and nobody attempting to wedge themselves between closing doors.
Instead, two crimson-and-cream carriages of a distant vintage wait beside a strip of grass at Braye Road, their windows open to the warm air of the English Channel. Dating from 1959, this train looks as though she has pulled herself away from a breakers yard in the dead of night and decided to spend her retirement by the sea.
I climb aboard and settle into a familiar London Underground seat. The carriage has the proportions of the capital; the low ceiling, curved roof and doors positioned ready for a commuter surge. But outside is a remote, Channel Islands collage of secluded coves, Georgian cottages and windblown greenery.
With a cough from the engine that sounds like poultry being startled, we move off at roughly the speed of an ambling sausage dog. The old Underground cars rattle past the harbour, Victorian fortifications and the pale scar of a quarry, travelling on rails laid not for tourists but to carry stone for Alderney’s monumental 19th-century breakwater.
The carriages, incredibly, were still trundling up and down the Northern Line until 1999, though their crimson-and-cream heritage paintwork, applied as part of an Underground centenary celebration, makes them appear far older than their 66 years.
My destination is Mannez Lighthouse, my only company a handful of bemused tourists and the gulls suspended in the air beyond the glass.
Alderney specialises in this kind of temporal dislocation. The northernmost of the Channel Islands is only a few miles long and has a population of barely 2,000, yet it appears to contain several centuries at once. There are Roman walls, Napoleonic signal towers, Victorian forts and German bunkers; Georgian houses and a tiny airport where the twin-prop planes seem to have been selected by a committee of Airfix model-makers.
Britain is present here (the Channel Islands are geographically of the British Isles but politically not part of the United Kingdom), but everything is very slightly out of kilter.
The post boxes are the classic British design, but are painted blue, not red. Some of the cars on the island are of an abnormally advanced vintage, still able to traverse the narrow lanes of Alderney due to the absence of any MOT requirements on the island. While the presence of Normandy, eight miles away, makes itself felt in the street names, the egg-yolk coloured butter and the iridescent quality of the light that, at sunset, bleach the sky hues of blood orange, rose wine and fuchsia.
