A new 12-sided one pound coin based on the threepenny bit is being unveiled - and is said to be the hardest in the world to fake.

Described as a "giant leap into the future" the new coin will replace the old one, after the Treasury announced that 3 per cent in circulation are fake - a total of more than 45 million.

The coin is based on the historic three pence piece, also known as the 'Threepenny bit', which was the first coin to feature a portrait of Queen Elizabeth II.

But unlike its predecessor, the new coin - which will be roughly the same size as the existing one when introduced in 2017 - will contain an array of technological advances making it difficult to forge.

As well as a 'bi-metallic' construction similar to the existing £2 coin, the new £1 will also feature new banknote-strength security pioneered at the Royal Mint's headquarters in Llantrisant, South Wales.

A Treasury spokesman said: "After 30 years loyal service, the time is right to retire the current £1 coin and replace it with the most secure coin in the world.

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

"We are particularly pleased that the coin will take a giant leap into the future, using cutting edge British technology while at the same time, paying a fitting tribute to past in the 12-sided design of the iconic threepenny bit."

As with all coins, the Queen's effigy will be on the 'heads' side, but the Treasury has said there will be a public competition to decide the design for the 'tails' side.

National Crime Agency counterfeiting expert John Sheridan said: "The issuing of a new coin with enhanced security features will make it more difficult for criminals to copy as well as presenting increased opportunities for law enforcement to investigate and disrupt the producers and distributors of counterfeit currency."

The coin will be announced as part of Chancellor Osborne's budget speech today. 

Do you like the new £1 coin or do you think it should be kept round? Let us know below.