"The website has been down since yesterday because of a problem with Cable & Wireless and the impact is that customers cannot access the site," a spokeswoman told vnunet.com.
"Cable & Wireless provides our network and the problem is down to a serious fault at its end."
The spokeswoman added that the fault had affected about 50 other companies which also have their networks provided by Cable & Wireless.
"Things are being rerouted at the moment and some customers have intermittent access to the website," she explained.
Martin Stern, head of internet performance firm Keynote UK, said that many existing and prospective clients who tried to access Egg.com will have suffered a long wait before being thrown into a search engine or a blank page.
"It is imperative that a company whose total business model is based on online presence manages to maintain consistent website performance," he said.
"It's not like Egg is simply looking after people's holidays or travel. In its own words this is 'Your Money', which in this day and age customers expect to access 24 hours a day."
Stern added that because Egg is an online-only bank with no branches and lower operating costs, it should be able to fund the building of a world-class online infrastructure.
Egg said that customers could still access their accounts by phoning its call centre on 08451 233 233.
"August is a quieter time for us on the website as so many people are on holiday," the Egg spokeswoman said.
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