The new longer-lasting notes - printed on polymer rather than paper and carrying the portrait of former Prime Minister Winston Churchill - are fetching hundreds of pounds online.
The first notes to be printed have a serial number starting with AA01, followed by six digits.
Not all of the notes have made it into circulation yet, so it’s possible that lower-numbered notes may still appear in cash machines before they make it onto auction websites.
The Queen already has the first of the notes, AA01 000001. Of the 440 million notes being released into circulation, there are a further 999,999 bearing the AA01 prefix .
If you don’t have one of the collectors items, the Bank of England is auctioning off a batch of low serial number banknotes at a charity event on October 3.
However, the lowest, with serial number AA01 000017, is expected to fetch around Â£1,000 - so you might want to just keep checking your change instead.