pilot16,
I flew from Stapleford just over a month ago, the advice I was given was to take the tube to Debden and then take the bus. I can't remember the bus route I was suggested as I've since thrown the post-it note that I wrote this information down on, away.
I have to agree with stiknruda to a certain degree. Have you contacted the airfield to find out which bus routes pass by or near the airfield, or even driven to it with your dad and researched the area around it for yourself?