People trying to order official documents such as passports, car tax discs or book driving tests are being duped and left out of pocket by fraudsters who have mocked up sites which seem like the genuine government version.
The National Trading Standards Board (NTSB) said the five arrests made last week were under the Fraud Act and for consumer protection from unfair trading regulations. All five people are on police bail.
It comes after more than 5,700 complaints, largely to do with cons involving tax returns, driving licences and passports, were made to Citizens' Advice and to the Advertising Standards Authority (ASA).
In an effort to force the fraudsters out of business NTSB chairman Lord Harris said its eCrime team is now "making it as difficult as possible for these online hoaxers to operate" and the government today launches an awareness campaign.
It includes a video warning people to be alert to the misleading websites. They often use URLs that include fragments such as 'govuk', 'directgov' or relevant organisation names.
Lord Harris said: "We have been working with search engines such as Google and Bing to remove adverts from online search results and we continue to gather intelligence across the country to help tackle this issue.
"We urge you to avoid unofficial websites which could leave you out of pocket or at risk of identity theft. Only use the GOV.UK website to find government services. If you come across copycat websites, report them to Citizens' Advice."