Internet users face regular “brownouts” that will freeze their computers as capacity runs out in cyberspace, according to research to be published later this year.

Experts predict that consumer demand, already growing at 60 per cent a year, will start to exceed supply from as early as next year because of more people working online and the soaring popularity of bandwidth-hungry websites such as YouTube and services such as the BBC’s iPlayer.

It will initially lead to computers being disrupted and going offline for several minutes at a time. From 2012, however, PCs and laptops are likely to operate at a much reduced speed, rendering the internet an “unreliable toy”.

When Sir Tim Berners-Lee, the British scientist, wrote the code that transformed a private computer network into the world wide web in 1989, the internet appeared to be a limitless resource. However, a report being compiled by Nemertes Research, a respected American think-tank, will warn that the web has reached a critical point and that even the recession has failed to stave off impending problems.

“With more people working or looking for work from home, or using their PCs more for cheap entertainment, demand could double in 2009,” said Ted Ritter, a Nemertes analyst. “At best, we see the [economic] slowdown delaying the fractures for maybe a year.”

In America, telecoms companies are spending £40 billion a year upgrading cables and supercomputers to increase capacity, while in Britain proposals to replace copper cabling across part of the network with fibreoptic wires would cost at least £5 billion.

Yet sites such as YouTube, the video-sharing service launched in 2005, which has exploded in popularity, can throw the most ambitious plans into disarray.

The amount of traffic generated each month by YouTube is now equivalent to the amount of traffic generated across the entire internet in all of 2000.

The extent of its popularity is indicated by the 100 million people who have logged on to the site to see the talent show contestant Susan Boyle in the past three weeks.

Another so-called “net bomb” being studied by Nemertes is BBC iPlayer, which allows viewers to watch high-definition television on their computers. In February there were more than 35 million requests for shows and iPlayer now accounts for 5 per cent of all UK internet traffic.

Analysts express such traffic in exabytes – a quintillion (or a million trillion) bytes or units of computer data. One exabyte is equivalent to 50,000 years’ worth of DVD-quality data.

Monthly traffic across the internet is running at about eight exabytes. A recent study by the University of Minnesota estimated that traffic was growing by at least 60 per cent a year, although that did not take into account plans for greater internet access in China and India.

While the net itself will ultimately survive, Ritter said that waves of disruption would begin to emerge next year, when computers would jitter and freeze. This would be followed by “brownouts” – a combination of temporary freezing and computers being reduced to a slow speed.

Ritter’s report will warn that an unreliable internet is merely a toy. “For business purposes, such as delivering medical records between hospitals in real time, it’s useless,” he said.

“Today people know how home computers slow down when the kids get back from school and start playing games, but by 2012 that traffic jam could last all day long.”

Engineers are already preparing for the worst. While some are planning a lightning-fast parallel network called “the grid”, others are building “caches”, private computer stations where popular entertainments are stored on local PCs rather than sent through the global backbone.

Telephone companies want to recoup escalating costs by increasing prices for “net hogs” who use more than their share of capacity.

Additional reporting: Adam Lewitt