NTL:Telewest, the UK's cable broadband operator, has suffered a serious breakdown in its service.
Many customers across its former Telewest franchise area tried to logged onto the internet on both Monday and Tuesday and found their broadband connection unavailable or performing poorly.
The problem was caused by a loss of synchronisation of dynamic customer IP addresses. Anyone who turned off the power to their modem during the outage period could have been affected, the company says.
A spokeswoman told ZDNet UK that the outage mainly affected customers in Birmingham, Yorkshire, the Northeast and the Northwest.
However, customers in London are also known to be affected and the company's website declared the incident to be national.
The problem arose around 4pm on Monday afternoon. The spokeswoman claimed that affected users were reconnected by 9pm on Monday. However, one NTL:Telewest user told ZDNet UK of continuing problems around 9am on Tuesday morning.
The cable operator's status page declared the service was not fixed until 9:11am on Tuesday.
NTL:Telewest says only 2,000 to 3,000 users out of its five million-strong customer base were affected. Engineers are still investigated the problem.
The failure follows NTL:Telewest network problems on Monday in Glasgow and Shropshire. The company says the incidents are not related. NTL:Telewest was formed last year, when the UK's two cable companies merged. Customers in the former NTL franchise area were not affected by the synchronisation issues.