I'm pretty sure about this one. I believe it is "Piccadillly"Piccadilly Circus" by Chris Beckett, originally published in Interzone magazine May-June 2005 and later in The Year’s Best Science Fiction, 23rd Annual Collection, which the author has kindly put online here. The story is a sequel to "The Perimeter" (online here). In the stories the inhabitants of the virtual London haven't been uploaded or digitised - they're actually disembodied brains all stored in a vast building just outside London.
From a review:
A near-future London is the setting, and for Clarissa Fell it is decaying decaying, dark and lifeless. However, for the rest of the population, now now uploaded into an Urban Consensual Field, the virtual London which they they inhabit, still largely co-terminous with the bricks and mortar reality reality, is still a vibrant, brightly lit place. Clarissa is determined determined to visit Picadilly Circus, to see the lights she saw as a child child – the real lights – and she is pottering into central London, her her Implants enabling her, when she chooses, to be part of the virtual London London. Beckett effectively illustrates, as she flicks between the dark dark, lonely London which she inhabits.