BBC Internet Correspondent Chris Nuttall: Surprised by the blackout

The trouble began on Sunday when a transatlantic cable was severed and back-up systems also failed. This left Britain's largest network, the Joint Academic Network (Janet), unable to communicate with North America for over 24 hours.

The breakdown brought immediate criticism from Janet's operator, the UK Academic and Research Network.

Its production services director, Dr Ian Smith, told BBC News Online: "Clearly we were not happy that it took so long to restore."

He believes it is "realistic to expect the Internet to be robust, but everything depends on what you have under the Atlantic."

No repeat

He points out that far more robust, "super-redundant" cables will be in use in the very near future, virtually eliminating the possibility of any repeat of the interruption to service.

"These are not single cables, but actually two separate cables routed hundreds of miles apart across the Atlantic. They can switch from one to the other automatically in just a few milliseconds. We hope to be on that in a couple of weeks."

Iceland is a staging point for some transatlantic cables

Two new "double" cables were laid last year - AC1 and Gemini. Gemini has UK landing points on the Gower, Wales, and in Cornwall and separate North American landing points. Separate cables also lead all the way up from the landing points to the service provider.

Automatic restoration of interrupted Internet service has received much attention but it is possible only if there is enough spare capacity. Dr Smith says the new cables will provide that.

"To have a fully redundant connection, you have to have double the capacity. You need the capacity you are using and that you would switch to. There's never been that before, but they have now deliberately designed it into the new cables."

Military system

The day-long Internet blackout came as a surprise. It had been widely believed that the Internet's origin as a military communication system meant it would survive even a nuclear assault. In fact, the severing of a transatlantic cable near Iceland was enough.

The Joint Academic Network (Janet), and some other networks, were affected. Janet is used by UK higher education and is the largest network in Britain.

Teleglobe International operate the cable which Janet uses and said that service had been restored by late afternoon on Monday. Normally, Internet traffic would be re-directed via another cable but Teleglobe said this did not happen because the volume of traffic was too high. They were unable to comment further.

Teleglobe owns one of world's most extensive Internet backbones, which is used by over 100 Internet service providers from 71 countries.