I think I read somewhere this week that the new stock ordered for the
Circle and Edgeware road branch of the District lines were going to have
one extra carriage, and therefore have a passenger capacity. Up from 6
cards to 7 if I remember correctly.

IS this going to involve a lot of platform lengthening, and if so where?

If not, then why wasn't this done years ago?

Or, (cynicism creeping in here) are they going to make a train from 7
short cars instead of 6 longer ones?