The B500 is a short B-road in central London.
It starts on Holborn Circus - a place where six roads and five different road numbers meet. The road then heads northeast along Charterhouse Street (along the boundary of the City of London) before ending at the next road junction: a set of traffic lights on the A201 Farringdon Street.
At one time the B500 continued along the remainder of Charterhouse Street, meeting the B501 and ending on the A1 Aldersgate. This section is now unclassified.
The B500 is described in the 1922 Road Lists
as London (Charterhouse Street (parts))
and a look at maps of the time will show the road as two non-connected sections at either end of Charterhouse Street and apparently not connected to any other classified roads. This is due to a quirk of the 1922 numbering system, in that there were no classified roads in the City of London. The parts of Charterhouse Street that did become the B500 in 1922 were outside the City. It was not until later when classified roads were able to enter the City that the B500 became a single route.