As I left work tonight, my mind was struggling over whether I should buy take-away dinner or what I should make for myself. So involved was I in this trifle, that I barely registered that there was something glaringly wrong with the picture to my left: Amidst all the faceless suits marching towards Victoria Station was a small, hunched figure, scurrying around in summery pyjamas. Even once I had registered the plight of this small being, societal indoctrination kept me on the straight and narrow path ahead of me. I was a tourist in Humanityville.

I praise God that she had more courage and approached me. She taught me that Victoria Street on a rainy February evening in summer pyjamas is preferable to a heroin detox clinic. I hope I am never in a position to confirm or deny that teaching. All she wanted was a few pence to spend the night in a Bed & Breakfast in Camden.

Society has taught me not to give money to homeless people because they use it for alcohol and drugs. Reading the Big Issue has taught me to help people to help themselves. I did my cowardly best and offered to buy her a ticket to Camden, on condition that she came with me to the station.

She said she was begging in Victoria so she could get enough money for Camden. Again I offered my conditional purchase of the ticket. Tears of frustration welled up in her eyes as she faced a person who wanted to help but offered a hindrance. It turns out that I am one of the fortunate majority who doesn't know that it is easier to beg for money in Victoria than it is in Camden. She was kind enough not to shatter the glass bubble in which I live by telling me.

She stood hunched and shivering before me, looking up at me through the tears in her big, beautiful eyes. I offered her my jumper and she accepted. But as I took off my bag, I realised that my jumper would not do her much good if she couldn't raise the cash to get off the street, so I offered her my coat instead. My £30 coat that I bought in Camden in October that was missing two buttons and about to lose a third.

The shivering birdlike frame in summer pyjamas told me I could not give it my coat. As I insisted I could, she continued to protest, and I felt ashamed. I thought about how all it had cost me was three hours' work. I thought about how the two jumpers I had underneath would keep me warm. I thought about how I could buy myself another on the way home if the fancy took me. I thought about how all she had on her tiny back was a pair of summer pyjamas and she was concerned about me giving up my coat.

As I helped her into it, we embraced. I'm not sure who hugged whom, but tears began to spill from my own eyes. Tears of shame; shame that I had not done more. Tears of brutal reality; remembering the one person I will always love more than most, who is a crack addict. Was she just a proxy for him? Would somebody give him a coat? Would I?

She was easy to hug: she was clean, small, eloquent, light-hearted. If she had been a six foot tall, aged man, who had not had the luxury of a shower for longer than either of us cared to imagine, what would I have done?

"God bless you" she said, "You have a good heart."

"So do you" I replied, as she went off ahead of me, drowned in my coat.

Then she came back: "God bless you" she said, "You have a good heart."

She came back one more time, before she headed off back into the faceless sea of workers, swimming against the tide.

The tears continued to flow like rivers down my cheeks as I slipped back into the commuter stream making its way to Victoria Station. My head was held high, defying the workers to look me in the eye. I was lost in self-righteousness.

It was only when I got to Clapham Junction and I stood on the platform in my two jumpers, feeling the cold, that I realised how little I had done. She could have used my hat -- I have three more at home. But mostly I could have taken her to Camden and paid for her room. All it would have cost me is two hours' wages.

I stood on the platform and I prayed to God that she got enough money to take my coat back to Camden, because without enough money for the B&B, she is sure to cross paths with someone who will offer her enough of a hit that she won't feel the cold until morning. All that she has gained in her few days in rehab, that were worse than standing on the rainy cold street in summer pyjamas, would be washed away in one euphoric shot.

Tonight, as I close my eyes, I pray again to God, and I thank Him for the friends that will look after me, that I won't need them to, that she had the courage I lacked (she needs it more than I do), but most of all, I thank God that I am a tourist in the grim reality of survival.

If I see her tomorrow, what will I do?