Why are you still at the same place you've been for 5 years if you are underpaid?
I don't mean that as a dig of any kind, just trying to get an idea of what your motivations are. Maybe you really love it there aside from feeling underpaid, or maybe you don't feel like you have the adequate skills to make a move?
The job has been challenging/interesting/varied and fun basically. I have applied elsewhere and had a raise, but another raise is out of the question now. (Thanks for the replys btw)
Tell them you're unhappy with your salary, and that the quality of your work is suffering because of it. Word it as if the next option you have is to quit, unless they remedy it. Don't leave on a bad note, and don't burn bridges, but keep that treatment of you in the back of your head.
I don't mean that as a dig of any kind, just trying to get an idea of what your motivations are. Maybe you really love it there aside from feeling underpaid, or maybe you don't feel like you have the adequate skills to make a move?