jonmorris wrote:

The service frequency from King's Cross to Blackfriars makes it almost
as good as any other tube line, but I bet loads of people never
consider it (and not having it on the tube map probably doesn't
help!).

Indeed. The other day I happened to be at a Lib Dem transport policy launch
(in my students' union capacity) and one person asked about the possibility
of reviving plans to extend the Northern Line to Sutton, giving as his
example getting to King's Cross. He was a little taken aback when it was
pointed out there is a direct train service!