A new 12-sided £1 coin enters circulation today (March 28), as it starts to edge out the old "round pound" after more than 30 years.

The new coin has been described as the most secure coin 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 coin-operated machines, as some will not immediately accept the new coin.

They may find themselves rifling through their wallets for an old round pound.

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 per cent 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.

Jonathan Hart, chief executive of the AVA, said the upgrades needed for the new £1 coin will cost the vending industry an estimated £32 million.

He said: "We support the Royal Mint and the Treasury's actions to protect the integrity of currency in the UK and reduce the level of fake coins in operation."

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.

The Government has previously described the new coin as "harder to counterfeit than ever before".

People have been urged to return their old round pounds before they eventually lose their legal tender status. They can bank them or spend them.

Around £1.3 billion worth of coins are stored in savings jars across the country, and the current £1 coin is thought to account for nearly a third of these.

Why is it being introduced?

There have been concerns about the old round pound's vulnerability to sophisticated counterfeiters - around one in every 30 round pounds is a dud. The new £1 coin boasts new security features.

What security features does the new £1 coin have?

The features include its 12-sided shape, its bi-metallic structure with a gold-coloured outer ring and a silver-coloured inner ring and an image that changes from a "£" symbol to the number "1" when seen from different angles.

It also has micro lettering and milled edges.

What other features does it have?

The coin's design reflects England, Scotland, Wales and Northern Ireland, with a rose, a thistle, a leek and a shamrock.

The fifth coin portrait of the Queen, designed by Royal Mint coin designer Jody Clark, is featured.

The coin is thinner and lighter than the old coin but its diameter is slightly larger.

What is happening to the old coin?

There is a period of just over six months when the old round pound will still be accepted as legal tender alongside the new coin. People are being encouraged to return their coins before October 15.

They can bank them or spend them.

Some of the new £1 coins will be made from melted-down round pounds.