The TfL website says that this is due to a collapsed sewer, and will
be back to normal by February 12th.

I've just looked on the londonworks website and the projected end of
works is now 22nd Feb!

Frankly, this closure is doing my head in. It was supposed to have
been completed by MAY 2009 but it keeps on running. I don't know what
they're playing at, but it seems like Thames Water are the main
culprits. TFL say the delays so far have been because Thames Water
have got in to do their Victorian mains replacements; but now this
'sewer collapse' has put things back even further. At this rate the
proposed May 2010 opening for the new Tube station isn't going to
happen either.

Whenever I go past the site the only activity I tend to see from the
handful of workers they've deployed there seems to be to and from the
greasy spoon on the corner. They really don't care what havoc they're
causing to the area.