The last church I belonged to does a lot of social work in London, including running services for homeless and formerly homeless people. I have frequently heard the argument that churches shouldn't do this, because they will inevitably proselytise and it's catching people at their most vulnerable. However, that particular church has a long tradition of assisting people with their physical needs before talking to them about faith - and only then if they're interested. To me, that's truly Christian mission. YMMV!