His name is Alan. And I notice as he perches himself down next to me as I wait for my taxi that he is probably around the same age as my dad.
In a soft voice he asks if I'm okay, my morning medication not having kicked in yet I tell him I have Parkinson's. He shakes his head at the mis-justice in the world and asks how old I am.
He tells me he's homeless. He has been for the last seven years, the fallout of a failed relationship and family bereavements. He sleeps in the underpass that runs beneath the river, where at least he can get some shelter and some warmth.
He asks me what music I like. I struggle to think. I ask in return and he tells me Elvis. He's always loved Elvis his whole life. Then I ask a stupid, sad question, 'Do you ever get to listen to music any more?', and the minute it trips off my tongue I feel silly for asking it. He tells me he used to run a karaoke night. Now on the weekends he dodges abuse from drunk strangers. I feel ashamed, to have the gift of music whenever I want it and, when asked, not be able to think of a single song I like.
I ask him whether he would be embarrassed if I gave him my sandwich, the one I've just bought at Waitrose. He says he can't take it, he'll only worry what i'll have for lunch. I make an excuse about having a work lunch so that he will take it. I wish I had bought something better than chicken and stuffing.
As he gets up to leave, the sandwich tucked into a carrier bag of all his belongings, he hugs my arm with genuine affection, he's clearly concerned about me, and I'm clearly concerned about him.
We are all just one bad decision, one family fallout, one unpaid rent away from being in his position. I think we forget that too often.
I hope I see Alan again.