Or seven for the Seventh World Congress, in Unity Theatre's parody of Green Grow the Rushes O, that we used to sing when I was a young thing. The line refers to the Seventh Congress of the Comintern, at which the popular front strategy was launched. There is also a variant line, 'seven for the stars on Connolly's plough', a reference to the starry plough flag of the Irish Citizen Army.
I keep running out of the main blog, but will briefly record here that yesterday I completed the Beachy Head marathon for the fourth time. This was my seventh marathon overall, and the last few miles are over the Seven sisters and Beachy Head. More details here: http://tomroper.typepad.com/marathon2005/
The link to the Unity Theatre above is to their Wikipedia entry. The Unity Theatre Trust's website at http://www.unitytheatre.org.uk/ seems unavailable.