A quiet, whispered "bravo" would have done, or a subtle nod of the head, but I did neither. Pity, and no doubt a testament to my Anglo-Saxon shyness.

Even at the time, I felt I should have done something, and I certainly do now; it virtually demanded recognition, after all it was an act of bravura that I've never seen before, or even heard about.

Two mornings ago, I was stood, back against one of the glass dividers, on a bouncing, rolling District Line train, reading the paper on my way to work. At every stop, more people got on, until it was the classic cheek by jowl London commuting experience.

A very handsome, wiry haired, well suited and booted man, jumped on the train at South Kensington. I'm guessing he was French, he had a soigne, elegance that no Brit could pull off for one thing, and for another, South Kensington is the 21st arrondissement; the quartier of choice for the expat French city high flyer

We were stood at roughly right angles to each other; he flicked through the FT, I concentrated on the Guardian. That's how we were for a few more stops, until he folded away the FT, and leaned over towards me, but not at me, looking at something that I could n't make out. He moved away for a second or so, then swayed back over again, gazing with hunter's intensity at something hidden behind a scrum of passengers by the other set of doors.

This happened two or three times, and always with the same focus. An absolute firmness of purpose. Until, the carriage started to empty, when there was enough space - and by this time I'm sure his mind was already made up -he turned around, steadied himself against the glass of the door, drew out a fountain pen and a business card, and wrote a short message on the back of it.

I caught a stray fragment of what he had written, when he turned back to face whoever it was he had in his sights, the first numbers of a mobile number and a half line about a woman in white boots. Remember I was too close not to see something and by now, my curiosity was razor sharp.

He had a nervous anticipation that I've really only ever seen when I've watched documentaries about beasts of prey eyeing an opportunity at the watering hole. Utter focus.

Eventually the tube thinned out and there was space between the remaining passengers. Very smartly, he stepped forward, tapped the shoulder of a young woman, with the deepest and thickest black hair I've seen in years, and passed his card over.

I could live forever if someone was to turn to me the way she did to him; a flashing look of amazement, then surprise, with the tiniest flush of embarrassment, then a smile strong enough to melt the Polar caps. This was her reaction to this act of beaumanship.

I should have applauded, done something to acknowledge this act of daring, passion, and romance. It was fabulous. A temerity that I would never dare, and yet one that I utterly admire.

Other than Le Chevalier and his Marianne, there was only her friend, who had just as a radiant a smile, and me, the silent witness, who were privy to any of this. What London missed that day.

The last I saw was the gallant knight leave the train at Mansion house a second or so in front of the black haired woman in white boots, and as the doors closed and the tube began to pull away, I saw them talking in what I hope was the breathless language of excitement.