Does CCTV work?

I am not a big fan of CCTV.  The UK is awash with CCTV, but it seems to have had no impact on the crime rate.

There is a pedestrian tunnel to the left of this photo - the entrance is hidden under that tree.  The tunnel goes under the railway line at Concord West station.  There are two CCTV cameras in the underpass, both monitored by RailCorp, yet every time I go through this tunnel, there is more graffiti in it.

If you ask me, CCTV is worthless unless you have people nearby that can respond very quickly to an incident and nab the people responsible.  If there is no one that can be on the scene within a few minutes, they are a waste of time and money.

In this case, no one from RailCorp even seems to have noticed that there is graffiti on their property (assuming RailCorp is responsible for the pedestrian underpass).  They'd be better off putting some effort into painting over graffiti as it appears, rather than putting up cameras which deter no one.  A camera is only any good if there is a reasonable chance of it leading to an immediate arrest.  I can understand them being used on trains, which have a Guard and possibly some Transit Police who can take action, or on a station which is staffed - but who is going to respond to an incident in an underpass like this?