“What are you going to do to save the world?" demands the girl. Not knowing what I am going to do, I say nothing and just look at her instead.
The girl is an exotic interloper in this locale. Her slogan T-shirt, camouflage anorak and radiantly healthy pink skin belong in the richer borough on the hill, where such looks and such opinions are commonplace. Down here, amid shops that simultaneously display - counterintuitively to non-locals, perhaps - chickens and mobile phones on hooks above plastic slabs, it is she who seems strange, not the fish from the waters of Africa and China that defrost on the slabs.
The girl is young, maybe 19. She holds a handful of damp leaflets that threaten to blow away in the north-easterly that hurls up the street, clattering drink cans against the kerb.
Behind her, several colleagues have set up a trestle table on which stacks of leaflets are balanced and a petition is taped down. The group's bicycles lean against the fence behind them and I wonder how they got the trestle table here.
“Sign the petition," she insists, "and fight climate change." Her optimism seems as misplaced as her appearance on this street. Registering my silence as either stupidity or antagonism towards her cause, the girl tuts, turns away and attempts to stop a fat African woman. The woman - shoulders hunched, bright printed robes and headdress flapping madly in the wind - walks on.
The girl turns back to me and declares in an accent that, if not cut-glass, is certainly bone china: "Climate change matters for everyone!" But no, it doesn't - not on this street, I fear. Here people are thinking about the price of food, the cost of accommodation, and their personal safety. Nonetheless here she is, and across the country there are thousands like her, throwing back the duvet in a centrally heated bedroom, bolting a slice of wholemeal toast, saying goodbye to Mummy and cycling to despondent high streets to try to browbeat the poor and the unwilling into supporting a proposition that looks ever more doubtful.
“Will you sign?" she asks, "It's to pressurise the US at Copenhagen." I try to sign, but the pen tears the wet paper and pushes it into a small pile of pulp. "It's all right." She pulls out a sheet of dry paper and holds a plastic bag over my hand. And for a moment this idealistic, enthusiastic, 19-year-old southern English girl seems to represent all that's best about Britain. But only a moment.