A new 12-sided £1 coin entered circulation today - with early teething problems expected at coin-operated machines across the country.
The new coin has been described as the most secure in the world and boasts high-tech features, including a hologram.
But consumers craving a snack or trying to park may face confusion when they attempt to pay at vending and ticket machines, as some will not immediately accept the new coin.
Tesco trolleys across many of its stores will be unlocked as the supermarket giant performs upgrades so that they can accept the new coin.
A Tesco spokesman said last week that "fewer than 200" of its stores will be affected.
The old coin and the new coin will co-exist together for a period of around six months, until the round pound ceases to be legal tender on October 15.
The new coins have been made at the Royal Mint in Llantrisant, South Wales, at a rate of three million per day.
They have a gold-coloured outer ring and a silver-coloured inner ring and are based on the design of the old 12-sided threepenny bit, which went out of circulation in 1971.
It might take a few days or weeks for people to start seeing the new £1 coins turn up in their change as they gradually filter into general use.
The Automatic Vending Association (AVA) estimates that when the new coin goes into circulation, around 85% of vending machines will be able to accept the new £1 coin and all will still accept the old coin.
It said that with around half a million vending machines across the UK, ensuring all of them are upgraded is a "major operation".
The body has estimated that all vending machines will be fully upgraded by the end of the transition period on October 15.
One pound coins were first launched on April 21 1983 to replace £1 notes. The Royal Mint has produced more than two billion round pound coins since that time.
The production of the new coins follows concerns about round pounds being vulnerable to sophisticated counterfeiters. Around one in every 30 £1 coins in people's change in recent years has been fake.