I'm not sure where Triumph was originally based, whether Birmingham or Coventry; but not Nottingham. Nottingham means Raleigh. Raleigh continued to sell "Triumph" labeled bikes well into the 1970's and even the 80's. Yours has typical Raleigh-pattern lugs, and the head badge says "Nottingham," so there is no doubt yours was made by Raleigh.

I would estimate early 70's based on the little I see. A serial number on the seat lug is consistent with that.

You should be able to look up the serial number as if it were a Raleigh serial number.