The north end of the Piccadilly line sounds so bucolic – Wood Green, followed in short succession by Bounds Green, Arnos Grove, Oakwood. So perhaps it was just a transformation waiting to happen. A surreal end to a no-longer-normal working day.

I blame the international flights at the other end of the line – something must have escaped and lurked in the train, all the way across London, waiting for the right moment to burgeon. Hot-housed by warm gusts of fetid underground air, gaining strength from other botanically-named stations, perhaps – Hyde Park, Green Park, Finsbury Park.

Wood Green – rural by name if not by nature – certainly provided the ultimate catalyst, because that’s when things finally became noticeable. Seeping through the dusty, metallic tunnel-smell came the verdant aroma of bolting vegetation. Slithering, rustling, creaking sounds smothered the whirr of the train’s motors.

As the rush-hour crowds on the north bound train thinned out, so the creeping, twining shoots were finally visible. Bold tendrils wrapped themselves around poles and strap-hangers; thickets of saplings sprang up between seats, evicting amazed passengers; a woodland glade established itself along the length of the carriages’ corridors. Doors failed to close as roots bridged the ubiquitous gap, branches thrust through ventilators and a leafy layer transformed the urban squalor into something far more beautiful.

It had been millennia since a forest had clad these north London slopes; and centuries since the locality was a rural backwater, far outside the city boundaries. But now, in an eerie process of metamorphosis, subtly shaded waves of green were rolling through underground tunnels and up through air shafts, reclaiming and transforming.

Wood Green was returning to its roots.