They all live in the same housing complex and work as cab drivers or cashiers. But what ''All or Nothing's'' three working-class London families mostly have in common is the enervating dreariness of their dead-end lives. Weighing them down with debt, depression, alcoholism, and unwanted pregnancy, writer-director Mike Leigh (''Secrets & Lies'') wallows a bit insistently. Yet all that misery, accompanied by mournful cellos, becomes almost mesmerizing, and Leigh's final flicker of hope is affectingly bittersweet. In the end, these people still have each other -- but that probably won't be enough.