We should all be paying close attention to small details on our banknotes after a King Charles III £5 note sold for thousands at auction.

The rare £5 note sold for £2,800 on the online auction site eBay, but what made it so valuable and how can you tell if you have one worth selling?

The serial number on the note is the key.

The £5 note sold on eBay had the serial number CA01 000046, making it extremely desirable for collectors.

(Image: Gareth Fuller/PA Wire)

The Sun explains: "Each new printed banknote features a unique "serial number" used to identify it.

"The serial number starts with a four-digit prefix followed by six digits.

"There are 999,000 notes printed and put into circulation - with the six digits at the end ranging from 000001 to 999000.

"Some of the new notes making their way into pockets are worth much more than their face value due to specific serial numbers they have on them."

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These are the prefixes, according to the news outlet, to look out for on each bank note which is an indicator as to whether or not they are valuable:

  • £10 notes - HB 01
  • £5 notes - CA 01
  • £20 note - EH 01 prefix (followed by a low number like 000002 or 000003)

Arnas Savickas, from auctioneers Spink and Son, speaking to The Sun added that serial numbers with solid blocks (for example 111111) are also worth a lot to collectors.

Five incredibly rare and valuable British coins

Rarest 50p coins in circulation the UK?

The Royal Mint has revealed the most valuable 50p coins in its collection.

The rarest is the Kew’s Garden 50p, which was designed to mark the 250th anniversary of the gardens in 2009. Only 210,000 coins were ever minted with this design.

The Kew Gardens 50p sells for £156.25 on average, but one seller received over £700 for one when they sold it on eBay.

The other rarest coins stem predominantly from the 2011 Olympics, with the wrestling, football and judo coins among the most valuable. Only 1.1million of each of these coins were produced.

Flopsy bunny and Peter Rabbit designs which were produced in 2018 are also highly valuable.

These coins - 1.4 million of which were minted - depict the characters from Beatrix Potter’s novels and celebrate the life of the English writer and these sell for around £5.

In 2019, 500 million coins were produced, with three new 50p designs.

These included one of Arthur Conan Doyle’s Sherlock Holmes, Paddington Bear at St Paul's Cathedral and the Tower of London.

Top 10 most valuable 50p coins, according to Royal Mint

Here is a list of the top 10 most valuable coins, when they were made and how many were minted:

  1. Kew Gardens (2009), 210,000
  2. Olympic Wrestling (2011), 1,129,500
  3. Olympic Football (2011), 1,161,500
  4. Olympic Judo (2011), 1,161,500
  5. Olympic Triathlon (2011), 1,163,500
  6. Peter Rabbit (2018), 1,400,000
  7. Flopsy Bunny (2018), 1,400,000
  8. Olympic Tennis (2011), 1,454,000
  9. Olympic Goalball (2011), 1,615,500
  10. Olympic Shooting (2011), 1,656,500