To conclude this thread, I never actually did the coolant change myself unfortunately.
After changing the o-rings on the bleed screw which seems to have fixed the leak, I was running out of time and light.
I could not for the life of me get the quick release for the bottom hose off to drain the system.
Perhaps if my hands were the size of grapes it may have been possible.
The only solution I could see at the time was to remove the bumper, but obviously that means removing the wheels, arch liners etc.
Alternatively, removing the fuse box and air box entirely would have helped with access to it.
I was also running out of time and light at that point and needed the car for work the next day.
So my patience wore thin and I phoned a trusted local garage that I've been using and he fitted me in the next morning.
I appreciate the advice you guys gave me though and hopefully it will help me in future.
I've also concluded the winter is just horrible. It's always too cold to do anything and gets dark before you can finish a job.