Chris. Free parking does start outside of a mile radius but I have found that the natives get a bit a**ey about non residents taking up their parking spaces outside of their houses. I have known them to use cones, crates etc to stop others using spaces.
As you drive in from the M3 and as you aproach Twickenham you will see a pub on your left called The Winning Post. They offer parking for £15, off road and secure, you can also exit the car park at the rear of the pub and miss some of the heavy after gig traffic.It is a 15 minute walk from here to the ground. If you go further towards the ground you will pass Richmond collage on your right, double back at the roundabout and you can park there. Be warned, the pirates were charging £25 the last time I was there and there is usually problems exiting and joining the main drag out.
All in all I prefer using The Winning post car park. It's your call whether a Yorkshireman is prepared to pay £15 to park a car;D