Each night as I leave the office, a colleague asks, "Have you got your hat pin?", but I've never yet felt threatened walking in London at night. Even in the smallest hours, it is hard to find a corner of the city in total darkness. Only once have nerves got the better of me. Leaving a party in Clerkenwell, I lost my way in deserted backstreets. With a flat phone battery and without an A-Z, I felt the beginnings of panic. It was January, damp and foggy and the cold was coming up through my soles. When, through a gap between brick warehouse conversions, I saw the dome of St Paul's against the moon, I almost wept with relief. 

Dickens's most distressing account of being out late without shelter is in Little Dorrit. Our heroine is locked out of the Marshalsea debtors' prison and she and the child-like Maggy are condemned to wander the streets until the gates open again at dawn. "In only five hours and a half," says Little Dorrit to Maggy, "we shall be able to go home." When dawn does come, her heart has been broken by exposure to the wet and cold, to shame, desertion and wretchedness.

Never allow yourself to get cold on a night walk. In "Down With the Tide", Dickens admires the pea coats worn by the night toll-takers on Southwark Bridge and the man from Waterloo Bridge "muffled up to the eyes in a thick shawl, and amply great-coated and fur-capped". However cold it is, there is always the promise of the kettle and a hot cup of tea back at my flat. 

Not so for everyone. In his journalism, Dickens returns again and again to the question of homelessness. In "A Nightly Scene in London" he describes a miserable evening, dark, muddy and raining. Outside the workhouse in Whitechapel he finds five slumped figures, shut out because there is no room: "Five great beehives, covered with rags — five dead bodies taken out of graves, tied neck and heels, and covered with rags — would have looked like those five bundles upon which the rain rained down in the public street." What, he asks, is to become of a society that leaves such desperate people there?

The most visible example of homelessness in London today is that of the Roma Gypsies on Park Lane. Is there anything that baits the tabloids as much as this conspicuous encampment in the West End? They have been moved on several times, but they return. Park Lane after midnight is a tale of two Londons. From the revolving doors of the grand hotels —the Dorchester, the Grosvenor House — men and women stumble out in hired black tie and long dresses. After too much free champagne at the company's annual beano, they hail taxis and put the receipts on expenses. Yards away, beneath the windows of estate agents advertising £12 million houses in Mayfair and Jaguar car dealerships, families of Roma Gypsies sleep on the pavement on mats of cardboard and old newspapers. Their possessions, piled into shopping trolleys, make wretched windbreaks. 

If you continue north of Park Lane onto the Edgware Road, the Roma are replaced by Albanians. Dressed in long skirts and headscarves, they beg for change along the strip of all-night shisha-pipe bars and kebab shops that gives this area the nickname "Little Beirut".