Woodford Station (Central Line) is about 5 mins jog/10 mins walk from the start. It is about half way round the first small lap which you can see on the course map. It would be a good idea to check whether there is going to be any planned engineeing work that weekend and in any case allow plenty of time.
The Ashton Playing Fields are on the A113 Chigwell Road, just north of where it passes under the M11. This is about 3/4 mile north of its junction with the A406 N Circular (Charlie Brown's Roundabout).
If you need the address/postcode for your SatNav, it is: 598 Chigwell Road, Woodford Green, Essex IG8 8AA
Note - If heading from the north on the M11 you need to get in the RIGHT hand lane when approaching the A406 and head WESTBOUND. At this point you are on a flyover above Charlie Browns Roundabout. You need to get off the A406 at the next junction and do a U-turn. Once back on the A406 (Eastbound), you need to keep left. You will then reach the roundabout at which point turn left towards Chigwell (A113). The Ashton Playing fields are on the left, just after the A113 passes under the M11.
Note that there is parking for about 200 cars at the Ashton Playing fields. This WILL get full after which point you will need to find a space in one of the many local residential roads.