Tom Anderson wrote:

and can trains from the [east] head south at Poplar?
Looking on the goggly maps, the shadow of
the HSBC building makes it hard to say

http://maps.live.com/default.aspx?v=...&scene=4268612

Such a service used to operate for much of the week. I can't remember
exactly, but I think it was between Tower Gateway and Beckton via a reversal
at Canary Wharf.