A crowd has gathered on the platforms, mostly male, mostly with cameras. A number of hi-vis staff are hovering, and peering westwards. The next Hammersmith train isn't due for 14 minutes.
Confirmation comes from a tannoy announcement, advising those who are here by accident that a steam train is due, and those who are here deliberately not to use flash photography and tripods. Everyone is standing politely behind the yellow line, in some cases arranged into a curve of photographers crouching across the platform. Some bloke near the main footbridge bursts into a rendition of "Ticket To Ride". Normally the assembled passengers would turn round and glare, but today is not normal, so they smile instead.
Not everyone is here willingly. An all-female family with suitcase and pushchair has attempted to follow the signs to the Bakerloo line and is lost at the top of the western footbridge. They don't give a damn that a steam train is due, they just want to get out of this rabbit warren and find their way to Marylebone. One of them goes off in search of a member of staff, which today is easier than usual, and they lug their way off of the platform just before the main spectacle appears.
After several false alarms from bog-standard trains, at last the approaching headlamps belong to the long-awaited loco. Those expecting huffing and puffing are disappointed. The purple engine rushes into the platform without pumping steam across the vaulted roof, and without stopping. A chain of heritage carriages follows through behind, filled with TfL staff and those deemed worthy of invitation. Chairman Boris is aboard, and a few who remember steam when it was normal, and some ladies who've had a jolly nice perm especially for the occasion. They beam collectively from the windows, as well they might, and rattle on.
The train is rounded off by an electric locomotive, the Sarah Siddons, inside which a group of volunteers is waiting to power the return journey. And then all too fast the train is gone, vanishing into the darkness of the tunnel ahead, leaving behind the faintest tang of steam in the air. The enthusiasts slowly disperse, some to the adjacent platforms, others by catching the ordinary train behind. Meanwhile those who were only ever here by chance wait patiently for an ordinary train, one that costs £2.10 rather than £150. TfL's normal Sunday service continues, almost like clockwork.
The 150th anniversary steam train is parked at Moorgate.
There are clues.
Some of the roundels have been replaced by lozenges. Police with sniffer dogs are patrolling the station. A hugecrowd of people is clogging the entrance to platform 4. All views of the steam train are blocked by a modern Hammersmith & City line train. Unless you've paid for a ticket, there is nothing to see.
The 150th anniversary steam train is due at Farringdon.
There are clues.
A crowd has gathered on the platforms, mostly male, mostly with cameras. A crowd has also clustered on the footbridges, and been allowed to stand on the stairs. "The heritage train is at Barbican", according to the station announcer.
Farringdon has attracted a much bigger crowd than at Baker Street. That's partly because there are more vantage points, and partly because the view's in daylight, but mostly because this is the first of today's runs that's been widely advertised. Most of those waiting are older rather than younger, including several couples and some with kids in tow. One man has pulled himself up from his wheelchair to stare over an unwashed patch of glass on the footbridge. According to the platform display the next train is "Not In Service" and only one minute away. Is that her, is she here?
This time it's Sarah Siddons leading the train. It's therefore not a proper steam journey, and those aboard have paid only £80 for their seats. The station is suddenly full of history and excited chatter and snapping lenses. But then, with impeccable timing, a Barking train pulls in on the opposite platform. Those standing here knew it was a risk, that their overview might be obscured at the crucial moment by a scheduled service. And so it proves, as the majority of the heritage train rolls by behind a veneer of 1960s ordinariness. Thankfully these trains are short, so those at the rear of the platform regain their view just as the back end passes by. Those further back are not so fortunate.
As the anniversary train passes beneath the last footbridge it lets rip a belch of steam, purely for decorative purposes because the engine's not powering this leg of the journey. The crowd are delighted, because this is what they've come to see - a cloud of anachronistic water vapour in a modern public space. Again the spectacle doesn't last long - all that waiting for at most a minute of action. But we saw the steam train in motion, which is more than those on board ever did, and we'll never forget its passing.