When Laurent Benson arrived in London from Belgium, on his to-do list was a trip to Threadneedle Street to exchange some old sterling at the Bank of England.

Little did he know that the timing of his errand on Wednesday meant he would be among the first to take possession of a new kind of banknote, the first to feature the image of King Charles and, for that reason, a bundle of cash likely to be worth a lot more than the number printed on the side.

“It’s just a complete random chance,” said Benson, 45, holding £50 in hand. He said he made the journey simply because he needed the cash rather than to collect a souvenir, even if the polymer banknotes felt like “Monopoly money” compared with the paper euros in his wallet.

“For me, who cares?” said Benson, who had first considered keeping an old bill featuring Queen Elizabeth. “For what? I’m not related to history of England.”

If a visit to the Bank was good fortune for some, for others, it was a calculated decision to snap up some of the collectible new currency.

Many queued outside the Bank in the early hours of Wednesday, according to staff, some eager to get their hands on the new notes.

By midday, listings of “authentic” King Charles banknotes started appearing on eBay, for double or in some cases triple their value.

The king’s portrait features on all four UK banknotes – the £5, £10, £20 and £50 – on the front and also in the see-through security windows. However, the other design and security features will remain the same, and no other changes have been made to the existing look of the notes.

“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,” said Andrew Bailey, the Bank’s governor.

For others, such as Ian Casey, the change was a good opportunity for gifts. After seeing news of the notes’ release on X, formerly Twitter, he paid a visit to the Bank in order to send cash to his four nieces in north Wales.

“I imagine it’ll probably take a little while for money to get out there, the new notes, so I thought I’d come and change them,” said the digital video journalist with the BBC, who plans to send £10 to each niece, keeping £70 for himself.

It’s also historic, he said: “It’s just a significant change in the times because most people in my family that are alive now have all known the Queen to be on notes. We’ve got in my family some notes that had the Queen’s father.”

Paul Whiting, 60, who expressed great affection for the late Queen, wanted to commemorate the day by exchanging his old banknotes on the first day of issue. “It’s kind of like a new era in a sense. It’s just nice to have some new money,” he said, after withdrawing notes of each denomination but stopping short of the £300 limit.

Whiting, a retired school teacher who lives in London, intends to keep the cash and show it to his elderly parents in Birmingham. “The country’s going through a lot of change and I think the monarchy offers a huge amount of stability and continuity but also change at the same time, and I think that’s a very special thing in this country,” he said.

“It’s just a change, isn’t it? I’ve still got this idea of the Queen and I suppose we’re moving into a new era – into the Charles era.”