Some of the new £5 notes featuring Winston Churchill are being snapped up by collectors for huge sums.

The Royal Mint has unveiled a very limited number of notes that feature a miniscule portrait of Jane Austen.

The fact the notes are so rare mean they could be worth an astonishing £20,000.

Graham Short, a micro engraver from Birmingham, was commissioned to etch the tiny 5mm image onto just four of the new polymer notes. It appears just next to the images of Sir Winston Churchill and Big Ben.

Classic quotes from Emma Pride and Prejudice and Mansfield Park have also been engraved on the notes. They went into circulation on December 4 and there is no special serial number to keep an eye out for.

Low serial numbers also selling for lots

Even if your aren't fortunate enough to find one of the 'Jane Austen' notes, there are a number of other polymer fivers that are proving popular with collectors.

Any notes from the initial batch of fivers printed by the Bank of England, which feature a serial number starting AA01, are regularly selling for hundreds of pounds online.

The first-ever note has the serial number AA01 000001 was given to the Queen, but there are 999,998 other new fivers with the AA01 prefix.

Tim Mitchell, a business owner from Llandudno, managed to get 30 new £5 polymer notes when he went to get change at the bank and expects to make at least £1,200 by selling them to collectors on eBay.

On October 3, the Bank of England auctioned a batch of low serial number new £5 notes for charity. One of the notes with the serial number AA01 000017, the lowest serial number note available to the public, sold for £4,150.

The Bank of England has donated some notes with significant, or low level, serial numbers to people and institutions that were involved in its development or that traditionally get one when a new series is launched.

The Queen was given the first note, while the Churchill War Rooms has been gifted the note AA01 001945.

[Read more: 11 ways to spot a fake Winston Churchill £5 note]

How to get one

Either visit a cashpoint that dispenses a fiver, head to your bank or spend in cash over the next few weeks to boost your chances of getting one.

The company distributing the new notes says it's still dispensing the new Churchill fivers and it could take until the end of next week before all cash machines are stocked up.

Around 5,200 ATMs dispense £5 notes according to the Bank of England and most have been adapted to handle the new polymer version.

Alternatively you could pick up a note at auction (and likely pay more).

On October 3, the Bank of England plans to auction a batch of low serial number £5 notes for charity.

One of the notes with the serial number AA01 000017 is expected to sell for between £800 and £1,200.

This is the lowest serial number note that will be available to the public.

The Bank of England has donated some notes with significant, or low level, serial numbers to people and institutions that were involved in its development or that traditionally get one when a new series is launched.

As mentioned earlier, the Queen was given the first note, while the Churchill War Rooms has been gifted the note AA01 001945.

Other notes that could be worth a fortune

There's a chance that the old paper £5 note will be worth more once it is phased out and withdrawn from circulation, so you may want to hold onto the ones you have now.

The old paper £5 notes featuring Elizabeth Fry will eventually be withdrawn from circulation on May 5 2017.

But there are other new notes due to be released that could also be valuable if you get one of the first batch.

More polymer notes on the way

From summer 2017, there will be a new £10 featuring novelist Jane Austen and from 2020 there will be a new £20 note carrying the image of artist JMW Turner.

Like the new Churchill fiver, the new notes will also be printed on polymer.

There are currently no plans to replace the £50 note that feature steam engine pioneers Matthew Boulton and James Watt.

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