I’ve been struggling with this one because it doesn’t look much sense on a modern map, so the only reason I can think is that the North Circular was nothing like it is today but carried the same traffic. We went to Keymarkets at Brandon a lot, particularly load and go so getting away mid morning or midday. Start at Paddock Wood.
Join the A 228 at Beltring go through East Peckham and up Seven mile Lane to the A20. Grind up the old Wrotham Hill and follow the A20 to Cliftons r/a at Eltham; right Westhorne ave and South Circular from Well Hall r/a and over the Woolwich Ferry. A117 and what is now South Woolwich Manor Way up to East Ham, left and very short right up East Ham High st to join the A116 across Wanstead Flats to Leytonston. Then A114 Whipps Cross rd across the bottom of Epping Forest to meet what is now the A104 but then IIRC it was the A11 Lee Bridge rd, and follow the A11 all the way through Epping Forest past Harlow and Bishops Stortford and turn off for Brandon at Mildenhall. ISTR that there was a good cafe on the A11 somewhere between passing Stanstead Muntfitchet and Saffron Walden?