There are quite a few unofficial parkway stations on or near the M25 or London motorways.
For example Kings Langley is 2 mins from J20, has a recent decked car park, and a half decent service. Then there are Potters Bar (4 mins from J24), Upminster (J27), Swanley (J3), Knockholt (J4), Caterham (J6), and Leatherhead (J9).
However many, many more people driving long distance on a radial route will park and ride from further out as the traffic gets worse the closer in you get. The best example is Micheldever (pop 1269) which has station usage of 125,000 pa; this is used by many people who drive up from the West Country but don't want to carry on the A303 / M3. Another example is Stansted Airport station which has people driving to it from all over the top half of East Anglia.