The new polymer £50 has now entered circulation, featuring an image of computer pioneer Alan Turing along with a number of groundbreaking security features.
This means every denomination of banknote now exists in plastic form, although paper £20s and £50s will still be accepted in shops until October 2022.
Here, Which? tells you everything you need to know about the Bank of England's most secure note yet.
The note entered circulation on 23 June to mark what would have been Turing's 109th birthday.
This completes the new line-up of polymer notes, which also includes a £5 featuring Winston Churchill, a £10 with Jane Austen and a £20 with JMW Turner.
Any paper £50 notes you have at home are still valid in shops, as are paper £20 notes. Both of these will be withdrawn after 30 September 2022. But that doesn't mean they'll become worthless.
Even after shops stop accepting them, many banks will still let you pay them in.
Then if your bank turns you away, the Bank of England honours every banknote ever printed, so you'll always be able to take or post your note to London to swap it for a new one.
Appropriately, considering Alan Turing's pivotal role in cracking Second World War codes, the Bank of England says the polymer £50 sits alongside the polymer £10 and £20 notes as the most secure it has produced.
Key security features include a hologram that changes between the words 'Fifty' and 'Pounds' when the note is tilted, and a number '50' that only appears under ultraviolet light.
Elements such as these make the note extremely difficult for criminals to duplicate, reducing the chances of fake notes entering circulation.
Alan Turing is a computing pioneer, a war hero and a gay icon.
He helped invent modern computing as we know it and helped end the Second World War through his work cracking the Enigma code.
After the war, Turing was convicted and inhumanely punished for having a relationship with another man, which was illegal at the time. Soon afterwards, in 1954, he took his own life.
In 2014, more than 50 years after he was convicted, Turing received a posthumous royal pardon in response to a high-profile campaign. This pardon was later extended to all men who were persecuted under now-abolished anti-gay laws with the introduction of a new rule known as the 'Alan Turing law'.
Unveiling the design earlier this year, the Bank of England's governor, Andrew Bailey, said: 'Alan Turing was a gay man, whose transformational work in the fields of computer science, codebreaking and developmental biology, was still not enough to spare him the appalling treatment to which he was subjected.
'By placing him on this new £50 banknote, we celebrate him for his achievements, and the values he symbolises, for which we can all be very proud.'
The switch from paper notes to plastic notes might not obviously be a sustainable one, but the Bank of England says all its polymer notes can be recycled.
In November 2019, the Which? Money Podcast visited a plant that recycles polymer £20 notes, turning them into plastic pellets that make household items such as plant pots.
Listen to the episode below to find out how it's done:
The Bank also says polymer notes last longer than paper notes and will stay in better condition throughout their use.
If you can't recall whose picture is on the old paper £50 note, you're not alone. (It's 18th century entrepreneur Matthew Boulton and engineer James Watt.) Of over four billion banknotes in circulation this year, only 357m are £50 notes. That's less than 10% of the total.
There's been some debate as to whether £50 notes even need to exist, and concern that they may be used primarily as part of the 'shadow economy', which includes crime.
In a special episode of the Which? Money Podcast, the team attempted to track down a 'missing £50bn' of lost cash, which includes many £50 notes. Listen here to find out how they got on:
You'll get an additional kick out of the note's design if you can read binary code. A ribbon next to Turing's portrait reads '1010111111110010110011000'. This converts to the decimal numbers 23061912, alluding to Turing's date of birth: 23/06/1912.
This Easter egg is just one of the many aspects of the design that reference Turing and his legacy.
There's no guarantee a rare note will ever be worth more than its legal tender, but that doesn't mean some of them won't end up catching collectors' eyes.
Avid currency collectors will want to get their hands on a new £50 note with a low serial number.
A note's serial number indicates when it was printed. Each time a new design enters circulation, the serial number changes to AA01 000001. Notes numbered close to that have been known to fetch large sums at auction.
Usually, the first three notes are presented to dignitaries. The 000001 and 000002 notes are always given to the Queen and Prince Philip, respectively.
Some collectors will also be on the lookout for the last paper £50 note ever printed, which will have the highest serial number instead of the lowest.
Which? research shows that there are two and a half million people in the UK who are reliant on cash to pay for essential products. A further seven million people say they would struggle without cash.
Despite the fact that 10 million aren't ready to lose access to cash, the cash network continues to shrink.
Since the start of 2020, 3,300 free-to-use cash machines have closed across the UK, with 431 banks closing over the same period, at the rate of a bank a day. The overall number of ATMs in the UK has fallen by almost 20% in the past three years from 67,300 to 54,400. The number of bank branches has fallen by 40% - from 9,900 to 6,000 - since 2015.
We're encouraging businesses to sign-up to the pledge, promising they'll accept cash as a payment method for consumers who want to keep using it. You can find out how to sign-up to the Which? Cash Friendly pledge on our .
This story was originally published on 2 April 2021. It was updated with details of the note's release on 28 June 2021.