The company made the announcement as part of its first-quarter results, and insisted that the job cuts were a necessary part of the ongoing integration of the NTL and Telewest businesses.
"The company forecasts that, as a result of the integration process, a total of 6,000 employees will leave the company before the end of 2007," the NTL Telewest statement said.
"Of these, it is anticipated that some 80 per cent will leave within the next 12 months."
NTL angered staff by responding to yesterday's press reports with a company memo describing the news as "speculation and not an official release", although the firm went on to say that the reports did include "some elements of truth".
"The memo to staff yesterday said there were elements of truth in the rumours," said a spokeswoman for NTL Telewest.
"Today we've gone into more detail and confirmed the integration plans in a comprehensive internal and external communications programme."
NTL had previously outsourced some of its telephone support to call centres in South Africa and India.
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