In message , at 14:50:41 on Sun, 23 Mar 2008,
Nick Leverton remarked:
Just watched the Poirot TV episode "Hickory Dickory Dock",
http://www.imdb.com/title/tt0182225/ London Underground interest included
the 1938 stock in pre-war red and cream livery, running in and out of
a station named "Hickory Fields". Where was the station though ?
I wasn't watching closely enough to see Tiled walls, but not a Tube -
it had a footbridge, and I think was open air or in a cutting - daylight
was visible along the running lines.

According to Barry Salter in 1999:

"Actually filmed at Arnos Grove (Piccadilly Line) with exterior
shots being shot *very* carefully either side of the bridge
where Bowes Road crosses the line.
--
Roland Perry