More Steam! Or What?

Do you know, I've never found out the real purpose of this contraption near the Excel in Docklands? I assume it must be some sort of pumping station, or to do with the tube. I't's been there while buildings have popped up around it - this photo dates back to a time when they were being built - I prefer it to a later version where they are built. Anyone know what it really is?

Away skiing, back after Christmas, pictures should continue if Blogger keeps working.