Police have arrested five people in connection with creating fraudulent copycat websites, designed to dupe users into thinking they were visiting official government sites.
The Advertising Standards Authority and Citizens Advice received almost 6,000 complaints about the websites, which were designed to charge people for tax returns, driving licences and passport applications.
Trading standards officials said those arrested have been released on bail pending an investigation.
Meanwhile, the government has promised to crack down on such websites and has warned the public to be vigilant when conducting official business online.
Lord Harris, chairman of the National Trading Standards Board, 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," he said.
Richard Lloyd, executive director of consumer group Which?, said: "For too long the people behind copycat websites have got away with misleading consumers into paying potentially hundreds of pounds for services that should be free.
"Simply punishing those committing this crime isn't enough, people who have been duped by these sites should also get a full refund of the money they were misled into paying."