It is an unwritten, or more precisely, an unspoken rule, known instinctively to all Londoners.

As paramount to survival in the great metropolis as never waiting for the lights to change at a zebra crossing. As infamous as the knowledge that you are never more than 300ft from a Pret A Manger. As dependable as the unsmiling face of the barista who serves you your morning coffee.

You don’t talk on the Tube.

The London Underground is a peculiar environment, the commuter’s sanatorium. Suits and Backpackers metonymically mingle here, on the great equaliser of Public Transport.

The chaos of the station platform billows through the sliding doors and is hushed.

London delights in its ambivalence, its ambiguity, its contradiction. The chaos and the hush.

I am not a native Londoner, but I go in and out of the city enough to know how it works. I obey the rules. I stand on the right of the escalator, and when someone stands on the left when I’m in a rush, I tell them where to go. But one day, when a friendly Northerner sat down next to me and struck up a conversation, I couldn’t give him the cold shoulder. He needed someone to explain the rules to him, someone to bring him into the fold.

Northern Guy: “So, where you going today?”

Me: “On my way home.”

Northern Guy: “Ah ok. So is it always like this? People don’t talk to each other in London?”

Me: “No mate, people don’t talk on the Tube.”

Northern Guy: “Oh, I’m sorry. I’m from Leeds, ya see.”

Me: “It’s fine, you weren’t to know.”

Silence.

Of course I did this without making eye contact with him. That’s a rule I’m not willing to compromise on.

There is only one instance in which discussion is acceptable: transport delays. The horror of your train screeching to a halt, then the tell-tale crackle of the speakers…

The echoing muffle of the train attendant through the overhead speakers – incomprehensible to the average human – will drag the quietest of carriages into audible grumbles. This is the signal to look up from your LCD screen or paperback book, emit a murmured curse and make eye contact with another disgruntled commuter.

This announcement is permission, nay, an invitation to make acquaintance with your fellow travellers, through mutual exasperation. Because, although we all abide by the Unspoken Rule, the truth is, many of us wish we could be like the Northern Guy. We wish we could make friends with the people we are sardined in with. But Heaven forfend anyone who causes a delay.

It is a truth universally acknowledged that a single man in possession of a good fortune, must get to his meeting on time. If Jane Austen’s Mr Darcy were to run up to the closing doors of a Bakerloo Line train at Piccadilly Circus, he would definitely be one of those arrogant wankers who uses their briefcase to keep the doors from closing. And our modern-day Lizzie, already sat demurely in the carriage, would be righteously pointing out his solipsism to her giggling companion, as they shuttled towards Charing Cross.

Of course this is only fiction.

People don’t giggle on the Tube.