It depends on how well you know him/her! If very well, use their usual first name; if not well at all, use "my Lord", "my Lady", "m'Lud", "your Lordship/Ladyship".
cheetos
http://www.post.japanpost.jp/int/question/45_en.html
As Senator , Representative , or Congressman or Congresswoman . You did not say State or Federal , or which house .
It would be appropriate to write, Dear Council Member J. Smith:
There is currently no English Parliament.