Image copyright Royal Mint

The new 12-sided £1 coin - which comes into circulation on Tuesday - has a hidden security feature to make it difficult to counterfeit.

It is thought to involve material inside the coin itself which can be detected when electronically scanned by coin-counting or payment machines.

But officials at the Royal Mint have not released any further details.

Other security measures include an image that works like a hologram, and micro-sized lettering inside both rims.

As a result, the Mint claims it will be the "most secure coin in the world".

It will replace the existing £1 coin, of which about one in 40 are thought to be fake.

"It's been designed to be fit for the future, using security features that aim to safeguard our currency, and currencies around the world, for years to come," said Adam Lawrence, chief executive of the Royal Mint.

Media playback is unsupported on your device Media caption A brief history of decimal coins

The old coin will remain legal tender until 15 October this year, after which shops are under no obligation to accept it.

After that date, consumers will have to take the coin to a bank to exchange it.

Supplies of the new coin have initially been delivered to 33 banks and post offices around the UK (see list below).

The new £1 coin: Vital statistics

Image copyright PA

Thickness: 2.8mm - thinner than old coin

Weight: 8.75g - lighter than old coin

Diameter: 23.43mm - larger than old coin

Number to enter circulation: 1.5 billion - about 23 per person. Old £1 coins will be melted down to make new ones

Outer ring: gold-coloured, made from nickel-brass

Inner ring: silver-coloured, made from nickel-plated alloy

Where can I get one?

To start with, supplies of the new coin have been delivered to 33 banks and post offices throughout the UK, including seven in Scotland, three in Wales and two in Northern Ireland.

They will gradually become more widespread over the next few weeks.

Lloyds Bank, which has the biggest branch network in the UK, said most of its customers would start to see the coins from Wednesday this week.

The coins will be available on Tuesday in the following towns and cities: