You may have seen already... but there is a tube strike this week and next week.
Around 9.30pm on Tuesday 4 February until the morning of Friday 7 February; and,
Around 9.30pm on Tuesday 11 February until the morning of Friday 14 February.
By the looks of things some tubes are running but they are on a reduced service- http://www.tfl.gov.uk/corporate/media/newscentre/29555.aspx (http://www.tfl.gov.uk/corporate/media/newscentre/29555.aspx)
Without sounding like BBC news- 'Check before you travel!'