Right, to update this. I've replaced both handbrake cables this evening. It's pretty straight forward to do. Unfortunately I didn't take any pictures however I will try my best to explain what I did.
Firstly, make sure the car is parked up and put on axle stands with the rear wheels removed and the handbrake off. Then, undo the cable adjuster fully under the centre console.
Then release the cable from the equalising piece.
Next, pull the cables through from underneath the car.
There are a series of metal clips that are really stiff. Best way to open these is with a screw driver and pair of pliers.
The cables will need a good tug to remove from the clips. Work down the car towards the rear brake. The passenger side cable runs under the exhaust heat shield. I just bent mine out of the way for better access.
Once at the caliper the end will be sized in. I used a spanner to wiggle it from side to side and it should come free.
Release the inner part of the cable from the caliper and remove.
That should be the cable completely off.
To put the new one in just follow the process in reverse making sure the rubber protectors are in the right place for the clamps.
Once the cable has run back to the hole and into the car it's just a case of fastening the cables back into the equaliser bar and screw it back onto the spring on the handbrake lever.
Hopefully that should be your lot. Any questions just ask.