Please check the following;

  1. Does your sash sit even all the way across the bottom on the sill when the window is closed?
  2. Does your top sash fit even across the top at the head when your window is closed?
  3. Is the gap on the woolpile down the side even at the top, middle, and bottom?

If you answered no to any of the above, then that could be why your windows are draughty.