( BrE )
a phrase like the man in the street , which means the average ordinary English person (of either sex). The phrase has been in use since the 1890s when the word ‘bus’ was already replacing ‘omnibus’. The choice of the bus from Clapham, an area of south-west London, has no special meaning; it is just a typical bus from a fairly ordinary place:
What will the man on the Clapham omnibus think of this new tax?