The publication date falls on what would have been the birthday of the computer pioneer and WWII codebreaker.
For the first time, the Bank's entire collection of currently printed banknotes is composed of plastic.
From October of next year, stores will no longer take paper £50 and £20 notes, however, post offices will still exchange them.
Any old notes can also be exchanged for their face value at the Bank of England's own counter.
Five million new banknotes may be printed in a single day, with 1.3 billion being printed annually. The site produces a variety of currencies, which are then shipped to countries all over the world.
Despite the fact that cash is being used less for purchases, there is still a high demand for banknotes, especially during the pandemic. The increased demand is due to a number of factors, including population growth and hoarding.
The Bank's stock of £50 notes is the least often utilized. Its future has been questioned in the past, with one assessment describing it as "the money of corrupt elites, all kinds of crime, and tax fraud."
However, 357 million of them were still in circulation this year, accounting for one out of every 13 banknotes.
"They're used a lot more than people realize," said Sarah John, the Bank of England's top cashier, whose signature appears on the note.
"A large portion of tourist expenditure is based on the £50."They're also employed as a means of storing value.
"The old paper £50 banknotes, which were initially issued in 2011, are no longer in production and will be phased out by September of next year. James Watt and Matthew Boulton, both pioneers of steam engines, are featured.
At the same time, paper £20 notes with the portrait of economist Adam Smith will be phased out. In February of last year, the new polymer version, which features artist JMW Turner, entered into circulation.
The polymer versions should last two and a half times as long as their predecessors, are more difficult to forge, and can withstand a wash cycle.
Concerns regarding plastic banknotes have been expressed, ranging from the use of animal products in their creation to anecdotal reports of the notes sticking in wallets and purses.
Producing polymer notes was "more complicated," according to Ruth Euling, managing director of De La Rue Currency, but it made financial sense.
"An important component of keeping cash alive is making it more efficient," she said.
Despite the fact that only a few ATMs are capable of dispensing £50 notes, a number of High Street banks have begun distributing the new denomination from their counters as of Wednesday.
The notice highlights and honours the accomplishments of Alan Turing, a Sherborne, Dorset native who helped speed up Allied efforts to decipher German naval messages encrypted with the Enigma machine, so shortening World War Two and saving lives.
He also played a key role in the early development of computers, initially at the National Physical Laboratory and then at the University of Manchester.
His inclusion on the note is also intended to promote diversity.
The Progress Pride flag will be flown above the Bank's building in London's Threadneedle Street on Wednesday to mark progress since his horrific treatment by the state because he is homosexual. He was granted a posthumous royal pardon in 2013 for his conviction for gross obscenity in 1952.
After being arrested for having an affair with a 19-year-old Manchester guy, he was compelled to take female hormones as a means of avoiding incarceration. He died when he was 41 years old. His death was ruled a suicide at an inquest.
The new note has security elements similar to past notes, such as holograms, see-through windows based partly on the imagery of the Bletchley Park codebreaking centre during WWII, and foil patches, in keeping with his work.
To commemorate Alan Turing's legacy, the UK's intelligence organization GCHQ has presented artwork of his portrait inside the wheels of the codebreaking British Bombe machine, which has been placed in the center of its headquarters.
"Alan Turing was a genius who helped to shorten the war and inspire the technologies that still defines our lives today," GCHQ director Jeremy Fleming said.
Snapchat has also made an augmented reality version of his art that it's possible to see in augmented reality.
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