Trolleys

For some time now I've noticed that there seems to be a large number of people who travel round the borough pulling trolley suitcases. As far as I know, Hackney is not a major transit point for travellers - we don't even have a Tube station. Who are they? Where do they come from? And more importantly, where do they go?
Maybe there's a particularly big itinerant population sofa surfing and forced to spend their days walking the cold and mean streets in search of warmth.
(If so, I'd try the library).