An American court has reversed parts of a $521 million (£265m) patent ruling against Microsoft, the software giant, and ordered a re-trial in a case that could have a huge impact on the future of the world wide web.

The case centres on a dispute over a key piece of software that allows web browsers - including Microsoft's market leading Internet Explorer (IE) - to work with other programmes such as audio and visual plug-ins.

Eolas Technologies and the University of California claim to hold a valid patent on the software and have charged Microsoft with illegally incorporating it into IE, which accounts for 90 per cent of the browser market.

The US federal appeals court this week overturned the previous $521 million ruling against Microsoft and ordered a lower court to re-try the case.

But according to W3C, the independent research body set up by Professor Tim Berners-Lee, the British scientist credited with inventing the world wide web in the late 1980s, if the patent were eventually upheld it would "cause cascades of incompatibility to ripple through the web". The group says that the code "provides critical flexibility to web browsers ... giving users seamless access to important features."

Prof Berners-Lee called for an urgent "re-examination of the ... patent in order to prevent substantial economic and technical damage to the operation of the world wide web".

Nearly every web user today relies on plug-in applications that add services such as streaming audio and video, advanced graphics and a variety of special purpose tools, W3C claims.

Macromedia Flash-powered animations, for example, commonly used on web pages, would not work without the software at the centre of the row.

To tackle the patent’s repercussions, billions of web pages would have to be modified by the introduction of a line of additional code.

In particular, W3C fears that online archives would risk being destroyed if funds could not be found to allow changes to be made to the programmes behind them.

"There is a fear that web managers faced with the prospect of modifying huge numbers of pages will simply delete them instead," Professor Michael Wilson of W3C's UK office told Times Online.

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