Crikey that's difficult. Surroundings' aren't salubrious enough to be the Fleet Ditch and the roadway (if that's what it is) is too wide.Looks like a sewer though. Is it Waterloo?
Mmm, that looks like a cut-and-cover for the London Underground - which would make it the Metropolitan line, if I remember rightly, which means I should be able to deduce where it is. But I can't without cheating. Do tell.
Is it Southwark, near London Bridge?
The answer, just guessed on Twitter, is Kingsway ... I believe a photo from the Aldwych, looking north, but I may be wrong on that ... taken by the London County Council during the build of the road and tramway ... see http://bit.ly/aJyK2p for more info.