The computer games industry has launched an unprecedented assault on illegal downloads, demanding payment from thousands of families who obtained the latest releases over the internet without paying.

Five of the world’s top games developers will serve notice on 25,000 people across the UK, requiring each one to pay £300 immediately to settle out of court. Those who refuse risk being taken to court. The companies will target their initial legal actions on 500 people who ignore the letters.

The companies involved – Atari, Topware Interactive, Reality Pump, Techland and Codemasters – make some of the popular games, including The Lord of the Rings,the Colin McRae Rally series and Operation Flashpoint. It is estimated that as many as six million people in Britain share games illegally over the internet. The aggressive action marks a dramatic change in the approach to copyright on the internet. The British music industry, hit hard by illegal file-sharing, has taken action against just 150 people in ten years.

The game makers have appointed the law firm Davenport Lyons. This week Isabela Barwinska, an unemployed mother of two, became the first person in the UK to be ordered to pay damages to a manufacturer. She must pay more than £16,000 to Topware after downloading Dream Pinball through a file-sharing site.

Roger Billens, a partner at Davenport Lyons, said: “Our clients were incensed by the level of illegal downloading. In the first 14 days since Topware Interactive released Dream Pinball 3D it sold 800 legitimate copies but was illegally downloaded 12,000 times. Hopefully people will think twice if they risk being taken to court.”

The law firm is applying to the High Court for an order requiring internet service providers to hand over the names and addresses of 25,000 individuals suspected of illegally downloading computer games. They have already obtained almost 5,000 addresses after providing evidence that illegal file-sharing had taken place. The move has provoked strong criticism within the games industry. A source close to the Entertainment and Leisure Software Publishers Association said that most publishers would be reluctant to bring legal actions against their “core market” and would be likely to look for other ways to minimise losses due to piracy.

Sales of computer games are predicted to reach £2 billion in the UK this year. Sales of consoles such as the Xbox 360 and Nintendo Wii are expected to hit 9.1 million, according to Screen Digest.

According to Peerland, which monitors games downloaded on three file-sharing websites, Operation Flashpoint was downloaded 691,324 times in one week. The most popular game was Battlefield 1942, which was accessed by almost 1.5 million people in seven days.