Rob, It depends on how the slack has occured.
Normal pad wear should not show up like that, so check the cables have not stretched or broken and that both of them are connected.
You can see them by lying down next to the car, but if you have access to a ramp its easier.
Chock the front wheels and get your G/F to operate the lever while you look to see whats going on.
If everything appears OK you should check the rear pads and if worn, replace them. Its not difficult and there is a guide on this site.
Adjusters need to be wound in to get the new pads in place and the handbrake cables disconnected while the footbrake is pumped to adjust the new pads back into place (this should be done with the engine running so the servo is working)
If you now connect up the handbrake cables and the lever is still travelling excessively, its new handbrake cable time.