and some more directions just in case anyone gets a bit lost
Travelling North M40 come off at Junc 5
Turn Right onto A40 back across the M40
Turn left onto A40 heading towards Aston Rowant and Postcombe (ie Northbound)
I am unsure what Junc 5 is like coming off but in theory you are picking up the A40 in the same direction as the M40 you have just left
As you approach Aston Woods there is a turning on the left hand side about .70 of a mile from the motorway, this should be Hill Road (unsure if it is marked) and will have Hill Farm Cottage at the junction
Follow this road back across the M40 and through the woods, you go through a left hand bend and Cowleaze Woods is on your left hand side with a carpark after almost 2 miles.
The road off the A40 to Cowleaze in effect will take you to Christmas Common and if you get here then you have gone too far!
Postcode OX49 5HU will take you just beyond the car park
Hope this helps!! 