Liverpool Central. Wednesday, 15th May. 7:20 pm.

All stations have an ebb and flow.  Passenger levels go up and down.  West Kirby is a lot busier on a sunny Sunday afternoon than a November weekday.  Hardly anyone ventures outside Sandhills' platforms for most of the week, until a football Saturday, when there are suddenly thousands pouring out the doors.

Britain's busiest underground station outside London is rarely quiet, but it does have its moments of calm.  Midweek, after the workers have gone home, before the revellers come out, there's a pause; the moment where tides turn and the waves are stilled.  The wide concourse, still clean and modern after its refurb, is empty.

There's a slap of flat shoes on the marble effect flooring and a group of middle-aged ladies come running through, coats flapping, clutching at their skirts to try and stop their hemlines from rising up.  The one at the back of the group has got overexcited from the thrill of the run for the train.  "Carol!" she bellows, too loudly, too prominently.  "Carol!"  And she giggles as they reach the ticket gates, even as her friends are shushing her.  They disappear down to the Northern Line but not before one more "Carol!".

Dotted around the edge are the waiters, the people loitering with intent, meeting friends, killing time until they have to be somewhere.  A girl in a sensible brown overcoat, big handbag, tapping at her mobile phone but glancing up at the ticket gates expectantly between keystrokes.  A student in shorts and a hoodie sat on the row of metal seats.  He's rocking back and forth, earbuds jammed in, eyes staring fixedly ahead.  Mindlessly killing time.

Beneath our feet a train rumbles in.  They're so close to the surface here; a firm kick downwards and you could make a hole in the floor to watch them pass.  The metal seats shudder under us, then a sigh of brakes and another set of passengers are disgorged.  Hefty men, no coats, good jumpers bought by wives, rubbing their hands together as they debate which pub to start their evening in.  A smart couple, he in a camel coat, her with trim hair and red lips, striding confidently out for the dinner date.  A gaggle of well-to-do old ladies off for a night at the theatre, chattering excitedly like children, a fog of flowery scent hanging around them.

This is the start of their night, but there are still people heading home; a guy with a man bag who's treated himself to a bag of chips after his day at the office, a young girl with thick rimmed spectacles who yawns as she waves her Trio at the guard.  A wizard strides in, six feet tall and resplendent in a long black overcoat and wide-brimmed hat.  His wife fizzes around him, a little ball of nervous energy, wearing a cape and panicking about their train.  They disappear into the MtoGo for their ticket; she dashes back out, almost running to the gates, but he's icy calm, taking giant strides and keeping pace with her.  The gate beeps twice as it burps their ticket out, the clatter as they pass through.

Underneath it all is the soft waterfall roll of the escalators.  A constant steady rhythm of movement.  The Selecta vending machine springs into life; a robotic arm scans the twirled shelves, surveying the Twixes and KitKats before stowing itself back in the hold.  The walkie-talkie of one of the Merseyrail staff parps out a sentence of fractured incomprehensible static; "Yeah.  Okay."

The students' mates have arrived, all of them dressed for football, a quartet of long shorts and lumpy sweatshirts.  They bond awkwardly, not quite bumping fists, but clearly ready to do so if the moment should arise.  His seat is taken by a trim lady with highlighted hair and a battered romantic saga.  She folds it back, cracking the spine for the fiftieth time, and begins to read.

Another train comes in, another group of excitement and fun.  A girl with two hula-hoops over her arm, black and gold; she wanders over to the cash machine and gets some money out, shifting the hoops round her body as though they're just a very large handbag.  The bouncing stride of a man with dreadlocks down to his waist, enjoying the rhythm of whatever is streaming into his headphones, walking a tricked out bike through the station.  The lady with highlights gets up and positions herself in front of the gates - the stream of passengers break around her like an island.  A woman of much the same age and much the same haircut is at the back of the crowd.  The two of them grin at one another, then kiss, then walk out of the station close to one another, sisters reunited in gossip and chatter.

Then it's quiet again, just the noise of the escalator, just the whistle of a staff member counting the minutes until the end of his shift, just the shuffle of feet of someone waiting for his friend.  Ebb and flow.