Dead currency. Replaced with the one pound coin.

I have dim memories of one pound notes from my very early childhood. They were phased out in 1983, as due to inflation their value was negligible, and coins are much more robust and less fiddly. The introduction of £1 coins meant that vending machines didn't have to have those awfully unreliable note-readers which I met while in America.

The final issue notes were small (about the size of modern-day £5 notes) and blue/green, with Queen Elizabeth II on one side (natch), and Sir Isaac Newton on the other.

All the maths textbooks I used at school featured £1 notes, which is probably why I remember them, seeing as I was two when they were phased out. A pleasing anachronism for a five year old. I seem to remember that the Bank of Scotland or Clydesdale Bank still issues £1 notes. Please /msg me if you can confirm/disprove this.