Alan Turing and NPL's Pilot ACE on the new £50 note

Alan Turing and his work, including NPL's Automatic Computing Engine (ACE) Pilot Machine, will be used in the imagery on the reverse of the new polymer £50 note that is expected to enter circulation by the end of 2021.

The Bank of England asked the public to offer suggestions for the scientist whose portrait should appear on the £50 note. In six weeks, the Bank received 227,299 nominations covering 989 eligible scientists. A shortlist was drawn up by a committee, including experts from the field of science, before a final decision was made.

Mark Carney, Governor of the Bank of England, commented: "Alan Turing was an outstanding mathematician whose work has had an enormous impact on how we live today. As the father of computer science and artificial intelligence, as well as war hero, Alan Turing's contributions were far ranging and path breaking. Turing is a giant on whose shoulders so many now stand."

Alan Turing provided the theoretical underpinnings for the modern computer. While best known for his work devising code-breaking machines during WWII, Turing played a pivotal role in the development of early computers first at NPL and later at the University of Manchester. He set the foundations for work on artificial intelligence by considering the question of whether machines could think. Turing was homosexual and was posthumously pardoned by the Queen having been convicted of gross indecency for his relationship with a man.

The shortlisted options demonstrate the breadth of scientific achievement in the UK, from astronomy to physics, chemistry to palaeontology, and mathematics to biochemistry. The shortlisted characters, or pairs of characters, considered were: Mary Anning, Paul Dirac, Rosalind Franklin, William Herschel and Caroline Herschel, Dorothy Hodgkin, Ada Lovelace and Charles Babbage, Stephen Hawking, James Clerk Maxwell, Srinivasa Ramanujan, Ernest Rutherford, Frederick Sanger and Alan Turing.

The new £50 Turing note will enter circulation by the end of 2021 and the design on the reverse of the note will feature:

• A photo of Turing taken in 1951 by Elliott & Fry which is part of the Photographs Collection at the National Portrait Gallery.
• The Automatic Computing Engine (ACE) Pilot Machine which was developed at NPL as the trial model of Turing's pioneering ACE design. The ACE was one of the first electronic stored-program digital computers.
• A table and mathematical formulae from Turing's seminal 1936 paper 'On Computable Numbers, with an application to the Entscheidungsproblem' Proceedings of the London Mathematical Society. This paper is widely recognised as being foundational for computer science. It sought to establish whether there could be a definitive method by which any theorem could be assessed as provable or not using a universal machine. It introduced the concept of a Turing machine as a thought experiment of how computers could operate.
• Technical drawings for the British Bombe, the machine specified by Turing and one of the primary tools used to break Enigma-enciphered messages during WWII.
• A quote from Alan Turing, given in an interview to The Times newspaper on 11 June 1949: "This is only a foretaste of what is to come, and only the shadow of what is going to be."
• Turing's signature from the visitors book at Bletchley Park in 1947, where he worked during WWII.
• Ticker tape depicting Alan Turing's birth date (23 June 1912) in binary code. The concept of a machine fed by binary tape featured in the Turing's 1936 paper.

Read more about Turing's work at NPL