Yes - head straight down that escalator. Instead of going through the ticket barriers there, head directly straight all the way along the corridor in front of you as you step off the escalator until you reach the next ticket hall and go through the barriers there. Then there is an escalator straight down to the Vic line platforms.
That escalator is often exit (there is only one), in which case I second the advice to use the entrance just outside the mainline station. As already mentioned, don't follow the signs or you might as well walk to Waterloo