Crispin Proctor:
If standing on the left side of the platform, looking down the tunnel
(Towards oncoming train) You can see a rail junction ...

Connecting track from the Northern Line, curiously named the King's
Cross Loop. See http://www.davros.org/rail/culg/northern.html.
It was opened in 1927 so that trains of what is now called the
Northern Line could be run to Acton Works for major maintenance.
--
Mark Brader, Toronto | "My ambition is to see a saying of mine attributed
| to Dorothy Parker or Mark Twain." -- Joe Fineman