"Martin Underwood" a@b wrote in
:

There are two ring roads around London.

Three. Besides the M25 and North/South Circulars, there's the inner ring
road, which is currently (almost) co-incident with the outer perimiter of
the congestion charge zone. Much like the North Circ used to be (and the
South Circ still is), it's a collection of roads that happen to form a
circumference around "central" London, rather than being a purpose-built
ring-road.

Iain