Could it be a version of The Two Butchers ? I seem to remember hearing one in which the robbers are dealt summary justice at the hands of the mob.

Incidently, your geography's crap Dai - Ratcliffe Highway now called just The Highway runs north of the Thames from Wapping to Limehouse, and until relatively recently, London Bridge was the river crossing furthest downstream. The Dover Road was the Roman Watling Street (The Old Kent Road - A2). The stretch from Blackheath to Shooters Hill was notorious for Highwaymen.