Morning raids were carried out at six locations across Sussex by 90 officers from the National Crime Agency (NCA).
The Times reported that the arrests were part of an investigation in to the forgery ring that led to HM Treasury scrapping the £1 coin.
The coin is being replaced from 2017 by a 12-sided version considered to be the hardest in the world for criminals to copy.
The new version will replace the current £1 coin which has been in circulation for more than 30 years.
The Treasury has said that advances in technology have made the current £1 coin more vulnerable to counterfeiters.
The NCA and the Royal Mint were unable to confirm the Times’ report as investigators held the four men and a woman this morning.
They were detained at five separate addresses on suspicion of importation, money laundering and offences under the Forgery Act.
A sixth property, a business premises, was searched in the Burgess Hill area of West Sussex, an NCA spokesman said.
Investigators from the Dutch fraud investigation service FIOD and an expert from the Royal Mint accompanied NCA officers.
NCA senior investigating officer Steve McIntyre said: “These arrests and searches were the latest phase of an ongoing international investigation looking in to the supply of fake currency from the Netherlands to the UK.
“This investigation follows the closure of a Dutch mint suspected of manufacturing counterfeit coins in November 2013.”
The five arrested – men aged 37 to 67 detained in Brighton, Burgess Hill and Hurstpierpoint, and a woman aged 42 held in Brighton – were bailed until July.
A Treasury spokesman said: “Over recent years, there has been an increase in the quantity of counterfeit £1 coins. The Treasury works closely with the Royal Mint, the National Crime Agency and the cash-handling industry to explore ways to maintain confidence in the currency and combat counterfeiting.
“After 30 years’ loyal service, we announced last year that the time is right to replace the current £1 coin with a new, highly secure coin that will reduce the costs of counterfeiting to our economy.
“The Government will ensure that the new design safeguards the integrity of our coinage for the future, and will employ the latest technology to make it the most secure circulating coin in the world.”