Police have busted a "sophisticated" factory printing fake copies of the new €20 banknote on an industrial scale - months after it was updated with new security measures to thwart counterfeiters.

Three men were arrested following raids in Italy in which €6.5m (£5.4m) of counterfeit cash was seized.

Public prosecutors said the forgers were using "sophisticated machines and state-of-the-art technology" in a Naples apartment - and their knock-off notes had included a cut-out for a replica hologram to be added later.

This is believed to be the first time investigators have found forgers producing copies of the new €20 note, which entered circulation in November.

The real bills include a transparent hologram that reveals a picture when held up to the light, and symbols which change colour when exposed to ultraviolet light.

The stash also included €50 and €100 bills. Lieutenant Colonel Guglielmo Sanicola said: "The fake bills don't need to be perfect, just good enough to trick the average consumer. And these were very high quality."

The old series of €20 notes, currently worth about £16.70, had been the most frequent target for fraudsters before they were replaced.

Close to half of the fakes withdrawn from circulation in the second half of 2015 were of this denomination.

Naples, which is Italy's third largest city, is a hotbed for counterfeiters, with millions of euros in fake bills seized there over the past two years.

Earlier this month, the European Central Bank unveiled a new €50 note to combat forgery.

And in May, the ECB announced plans to cease production of €500 notes amid concerns they are used by criminal gangs.