Brits have been told to keep a close eye on their bank notes after a new King Charles III £10 note sold for £17,000 at auction.

The charity auction event, held by Spink & Son on behalf of the Bank of England, featured 262 lots of new £10 notes featuring the face of King Charles III.

The new banknotes, the first to feature a sovereign other than Queen Elizabeth II, were released in June and will circulate alongside old notes featuring the former Queen.

In line with guidance from the Royal Household, the new notes will only be printed to replace those that are worn, and to meet any overall increase in demand.

Most valuable Bank of England notes

Certain serial numbers featured on the new notes are of particular value to collectors, with the lowest serial numbers often being the most attractive.

In April, the Bank of England revealed the lowest serial numbers of each denomination of the new King Charles notes.

They are:

  • £5: CA 01 000001
  • £10: HB 01 000001
  • £20: EH 01 000001
  • £50: AJ 01 000001

While those notes are in the possession of the King himself, other low serial number notes could be worth a small fortune.

At the charity auction, the £10 note featuring the serial number HB01 000002 caused a mini bidding war, as the winning bidder agreed to part with £17,000 to get their hands on it.

HB01 000003 sold for £5,500, while HB01 000004 sold for £2,400.

Arnas Savickas, head of banknotes at auctioneers Spink and Son, told the Mirror: "Depending on the serial number of the note - it's reasonable to assume that the lowest serial number of a £5 could fetch between £250 to £500, while £10 and £20 notes could go for £500 and £1,000 respectively.

"A £50 then could go for several thousand pounds. It's not impossible that outside of the auction, someone could find notes with a serial number within the first million. Outside of the auction, someone could potentially find a note with a serial number as low as six figures - you could probably get one with 100000."

New King Charles III bank notes

The portrait of Charles will appear on all four banknotes – the £5, £10, £20 and £50 – with no other alterations to the existing designs.

Bank of England Governor Andrew Bailey said: “We’re very pleased to be issuing the new King Charles banknotes.

“This is a historic moment, as it’s the first time we’ve changed the sovereign on our notes.

“We know that cash is important for many people, and we are committed to providing banknotes for as long as the public demand them. Bringing these new notes into circulation is a demonstration of that commitment.”

Although the Bank of England started to produce banknotes in the 17th century, Charles’s mother, Queen Elizabeth II, was the first British sovereign to be given the honour in 1960 on a £1 paper note.

Ross Borkett, banking director at the Post Office, said: “This historic launch of the new banknotes featuring King Charles III comes as we experience the highest levels of cash withdrawals and deposits in Post Office branches.

“We’re pleased to be able to mark this day by giving people the opportunity to withdraw the new notes from our branches.”

Banknotes featuring Queen Elizabeth II remain legal tender and there is no need to exchange them.