Britain said today it would withdraw the £1 coin it has used for the past three decades and replace it with a 12-sided piece that will be harder to fake.

The Treasury said the new coin, made of two metals in two different colours and modelled on the old Threepenny bit, will be "the most secure coin in circulation in the world".

About 3% of all £1 coins, about 45 million, are currently forgeries and in some parts of Britain this rises to 6%, according to the Royal Mint.

The new coin will have the same shape of the old "Threepenny bit" that was introduced in 1937 and went out with 
decimalisation in 1971.

It was popular during World War II when households and businesses had to abide by a blackout to thwart enemy bombings, because its distinctive size and shape made it easy to recognise in the dark.

The new £1 will be made using cutting-edge technology that allows it to be easily authenticated. Combined with the use of two metals and the 12 sides, the Royal Mint hopes it will be hard to counterfeit.

"After 30 years of loyal service, the time is right to retire the current £1 coin and replace it with the most secure coin in the world," said British Finance Minister George Osborne.

"With advances in technology making high value coins like the £1 every more vulnerable to counterfeiters, it's vital that we keep several paces ahead of the criminals to maintain the integrity of our currency," he added.

The new coin is expected to be in circulation by 2017, following a consultation with businesses.

As with all British coins, the "heads" side will feature the image of Queen Elizabeth II and there will be a public competition to decide the "tails" side.